net: Look up the local address if none is given

Look up the local IPv6 address if none is given by the application.
If no address is present, return a NULL context.

Change-Id: I7d4ef306944f65bc40799865dc6520b977636f6b
Signed-off-by: Patrik Flykt <patrik.flykt@linux.intel.com>
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>