doc: move IP porting guide to porting section

Move ip porting guide from the subsystem/networking section to the porting
section of the documentation.  Tweak the layout of the doc for improved
readable too.

Jira: ZEP-825

Change-Id: I688151f1da8862a783a82bcd4dde654c5178c30f
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/porting/ip-stack-migrate.rst

@@ -15,29 +15,33 @@ find more details in the network header file documentation in include/net/.
 Because of this new native IP stack, the following changes are required to
 migrate applications using the older v1.6 IP stack to the new v1.7 IP stack:
 
-* **Dual IPv6 and IPv4 stack support.** In Zephyr v1.6, applications could not
+Dual IPv6 and IPv4 stack support.
+  In Zephyr v1.6, applications could not
   use both IPv6 and IPv4 simultaneously. This is changed in Zephyr v1.7 and the
   IP stack supports both IPv6 and IPv4 at the same time. In practice this means
   that applications should be prepared to support both IPv6 and IPv4 in the
   code.
 
-* **Multiple simultaneous network technologies support.**
+Multiple simultaneous network technologies support.
   In Zephyr v1.7 it is possible to have multiple network technologies enabled
   at the same time. This means that applications can utilize concurrently e.g.,
   IEEE 802.15.4 and Bluetooth IP networking. The different network technologies
   are abstracted to network interfaces and there can be multiple network
   interfaces in the system depending on configuration.
 
-* **Network Kconfig options are changed.** Most of the networking configuration
+Network Kconfig options are changed.
+  Most of the networking configuration
   options are renamed. Please check the :ref:`networking` documentation for the
   new names.
 
-* **All uIP based APIs are gone.** Those APIs were not public in v1.6 but
+All uIP based APIs are gone.
+  Those APIs were not public in v1.6 but
   applications could call them anyway. These uIP APIs were mainly used to set
   IP address etc. management style operations. The new management APIs can be
   found in net_if.h and net_mgmt.h in Zephyr v1.7.
 
-* **Network buffer management is changed.** In earlier Zephyr versions, there
+Network buffer management is changed.
+  In earlier Zephyr versions, there
   were big 1280 byte long buffers that applications could utilize. In Zephyr
   v1.7 this is changed so that device memory is utilized more efficiently.
   Now small buffer fragments are allocated to store the data, and these
@@ -46,16 +50,19 @@ migrate applications using the older v1.6 IP stack to the new v1.7 IP stack:
   network is not contiguous and application should use the helper functions
   found in nbuf.h when reading and writing the network data.
 
-* **Network context/socket API is changed.** The new API found in net_context.h
+Network context/socket API is changed.
+  The new API found in net_context.h
   is more BSD-socket-like than the earlier API. The new context API is not
   fully BSD socket compatible as it needs to support both synchronous and
   asynchronous operations. Porting BSD socket application to use the
   net_context_* API is easier than in Zephyr v1.6.
 
-* **CoAP library API is changed.** The Zephyr v1.6 CoAP API is removed.
+CoAP library API is changed.
+  The Zephyr v1.6 CoAP API is removed.
   The new Zephyr v1.7 API is called ZoAP and it can be found in zoap.h header
   file.
 
-* **The TinyDTLS library is removed.** The tinydtls crypto library was used
+The TinyDTLS library is removed.
+  The tinydtls crypto library was used
   only by CoAP in Zephyr v1.6 and it is removed in Zephyr v1.7. It is replaced
   by mbedtls library.

doc/porting/porting.rst

@@ -11,3 +11,4 @@ architectures, SoCs and boards.
 
    arch.rst
    application.rst
+   ip-stack-migrate.rst

doc/subsystems/networking/networking.rst

@@ -11,7 +11,6 @@ operation of the stacks and how they were implemented.
    :maxdepth: 1
 
    overview.rst
-   ip-stack-migrate.rst
    ip-stack-architecture.rst
    networking-api-usage.rst
    l2-and-drivers.rst