- Fix 'badness in local_bh_enable' warning

   This involved moving dev_queue_xmit() calls
   outside of sections with spinlock held.

 - Fix 'fix old protocol handler' warning

   This includes accounting for shared skbs,
   setting protocol .data field to non-null,
   and adding per device synchronization to
   receive handler.

This has been tested in PPP and Cisco modes
with and with out the keepalives enabled
on a SMP machine.