test: af_packet: Add test for passing UDP packet to open RAW socket

The af_packet test has been augmented to check if sent UDP packet from
one port to another (via net interface) is also passed to open SOCK_RAW
connection.
The test_packet_sockets() function has been reused to setup the SOCK_RAW
sockets for this test.
It is important to note that the packet is passed to receive part of net
stack after being sent.

Signed-off-by: Lukasz Majewski <lukma@denx.de>