net: core: In RX check if the pkt is for loopback interface

If the loopback driver is enabled, then the packet might come
from localhost in which case mark it properly. Without this marking
the packet from/to 127.0.0.1 or ::1 would be dropped in later checks.

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