Switch to ETHER_INPUT2 on ethernet input path by default:

Switch to ETHER_INPUT2 on ethernet input path by default:
- Nuke old ether_input_chain and ether_demux_chain
- Nuke old vlan_input
- Nuke ETHER_INPUT2 kernel option
- Adjust comment about functions on old ether input path
- Adjust NIC drivers which aware ETHER_INPUT2

vlan(4):
Clearing of ifnet.if_vlantrunks is now protected in the following way
    trunks = ifp->if_vlantrunks;
    ifp->if_vlantrunks = NULL;
    netmsg_service_sync();
    kfree(trunks);
Users of ifnet.if_vlantrunks have already been adjusted to aware of this.

bridge(4):
Clearing of ifnet.if_bridge is now protected in the following way
    ifp->if_bridge = NULL;
    netmsg_service_sync();
Users of ifnet.if_bridge have already been adjusted to aware of this.

carp(4):
Remove the LK_NOWAIT lockmgr lock flags; using LK_NOWAIT was actually a
workaround for that lockmgr lock was used in NIC's interrupt routine
(i.e. old ether_input)
Dragonfly-bug: <http://bugs.dragonflybsd.org/issue957>

ipflow:
- Now per-cpu ipflow hash table installs its own ipflow entry instead of
  having ipflow entry duplicated onto each cpu
- Remove the serializer parameter to ipflow_fastforward()
- Comment out ipflow_fastforward() in ef(4) and ppp(4), they need to be
  changed to fit the current ipflow cpu localization model