Introduce ETHER_INPUT_CHAIN option:

Introduce ETHER_INPUT_CHAIN option:
1) During RXEOF, we aggregate packets, which have same target CPU, instead of
   calling lwkt_sendmsg() for each input packet.
2) At the end of RXEOF, low level ipiq sending is used to dispatch mbuf chain
   to the target CPU.
3) On the target CPU, the ipi function puts mbuf to their belonging msgport.
   Note, though lwkt_sendmsg() is used in ipi function, no further ipi activity
   will happen, since we are on target CPU.

em(4) is made to aware of this option.
This option is off by default and has no effect on vlan(4) operation.