bpf cleanup

[Sam Leffler]

http://people.freebsd.org/~sam/bpf.patch

has changes to eliminate the widespread use of stack-based mbufs for use with 
bpf.  The patch replaces them with a new bpf_mtap2 routine that does the 
right thing w/o exposing the internal workings of bpf.  I've restored the 
M_ASSERTVALID macro to BPF_MTAP but should probably just move this to the 
bpf_mtap/bpf_mtap2 routines.

Buried in this patch are also some changes to make consistent the prepending 
of the address family for some devices.  Previously some code was assuming 
sizeof(int) == sizeof(u_int) == 4 bytes; they've all been changed to use 
u_int32_t.

Pending feedback I'll commit this stuff after the freeze is lifted.

	Sam