replace the use of ifqueues for most input queues serviced by netisr

replace the use of ifqueues for most input queues serviced by netisr
with niqueues.

this change is so big because there's a lot of code that takes
pointers to different input queues (eg, ether_input picks between
ipv4, ipv6, pppoe, arp, and mpls input queues) and falls through
to code to enqueue packets against the pointer. if i changed only
one of the input queues id have to add sepearate code paths, one
for ifqueues and one for niqueues in each of these places

by flipping all these input queues at once i can keep the currently
common code common.

testing by mpi@ sthen@ and rafael zalamena
ok mpi@ sthen@ claudio@ henning@