net: yaip: Add send() to net_if API

The send() function is called from IP stack and it is used
when the network packet needs to be send via a specific
network interface.

Change-Id: Id6ce86b1748915fee73b62366dee13fcb7cf11a1
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>