XIA/Serval: accept local connections

Function serval_tcp_rcv_checks() didn't accept packets generated
localy and deivered through a loopback device.
Thus, Serval couldn't accept local connections.

Instead of adding loopback devices to the test, this patch drops
the whose test because XIP only passes packets to Serval
if Serval has recognized the next XIDs in those packets.
XIA/Serval: make control extension header optional

Control extension header is optional in SAL, but the code was
requiring this extension in order to choose source and
destination addresses of connected sockets before
transmitting packets.

This problem shows up after a connection is established.
Without source and destination addresses, the code was hitting
a BUG() call.
XIA/HID: adapt code to struct netdev_notifier_info

Jiri Pirko <jiri@resnulli.us> introduced struct
netdev_notifier_info in commit
"net: pass info struct via netdevice notifier".

Without this patch, principal HID would crash while loading.