RSTP testing - PATCH: source MAC address of BPDU

RSTP testing - PATCH: source MAC address of BPDU

   BPDU's were being sent out with an all zero source ethernet
   address. These packets don't make it far in the receive path on
   another bridge since bridge_handle_frame() checks for valid source
   ethernet address and drops them if that isn't the case.

   I needed to undo a change I made in rstplib/transmit.c, where I was
   not setting source MAC address because the LLC layer was doing it.

   TODO: We get notified when a port MAC address changes, so we should
   cache it. Right now it uses SIOCGIFHWADDR each time (for each BPDU
   sent) using a cached name, which is not good.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>