Add TLS credential management subsystem that enables to register TLS
credentials in the system. Once specific credentials are registered in
the system, they will be available for TLS secure sockets to use.
To use a TLS credential with a socket, the following steps have to be
taken:
1. TLS credential has to be registered in a system-wide pool, using the
API provided in "net/tls_credentials.h" header file.
2. TLS credential (and other TLS parameters) should be set on a socket
using setsockopt().
Note, that there is no need to repeat step 1 for different sockets using
the same credentials. Once TLS credential is registered in the system,
it can be used with mulitple sockets, as long as it's not deleted.
Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
d09cbcaf6f