[AF_UNIX]: Convert socks to unix_socks in scan_inflight, not in callbacks

The scan_inflight() routine scans through the unix sockets and calls
some passed callback. The fact is that all these callbacks work with
the unix_sock objects, not the sock ones, so make this conversion in
the scan_inflight() before calling the callbacks.

This removes one unneeded variable from the inc_inflight_move_tail().

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>