net: Explicitly include toolchain.h to check for endianness definitions.

This commit adds an explicit inclusion of toolchain.h from ptp_time.h.

The endianness preprocessor definitions (__BYTE_ORDER__,
__ORDER_LITTLE_ENDIAN__, __ORDER_BIG_ENDIAN__) are used by ptp_time.h;
these being not defined can easily go unnoticed and cause unexpected
behaviours, as detailed in PR #18922.

toolchain.h ensures that these preprocessor definitions are defined and
*must* be included in a file that uses these definitions.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

include/net/ptp_time.h

@@ -21,6 +21,7 @@
  */
 
 #include <net/net_core.h>
+#include <toolchain.h>
 
 #ifdef __cplusplus
 extern "C" {