[BRIDGE]: Unaligned access when comparing ethernet addresses

compare_ether_addr() implicitly requires that the addresses
passed are 2-bytes aligned in memory.

This is not true for br_stp_change_bridge_id() and
br_stp_recalculate_bridge_id() in which one of the addresses
is unsigned char *, and thus may not be 2-bytes aligned.

Signed-off-by: Evgeny Kravtsunov <emkravts@openvz.org>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Pavel Emelianov <xemul@openvz.org>