[LPF] use lpf/linux version of get_hw_addr for SO_BROADCAST sockets

We need a working version of get_hw_addr for use in sockets.c. So still
compile get_hw_addr if LPF is available but we don't use LPF_SEND or
LPF_RECEIVE.

This fixes a compile error on linux if configured with
USE_SOCKETS on linux.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>