o To prevent a race between RTM_DELETE message and   arptimer() deleting stale entry, we need to lock   rtentry before unlocking radix head.
o To prevent a race between RTM_DELETE message and
  arptimer() deleting stale entry, we need to lock
  rtentry before unlocking radix head.

Reviewed by:	sam

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase