socket addresses in mbufs. (Socket buffers are the one exception.) A number
of kernel APIs needed to get fixed in order to make this happen. Also,
fix three protocol families which kept PCBs in mbufs to not malloc them
instead. Delete some old compatibility cruft while we're at it, and add
some new routines in the in_cksum family.
Kernel Appletalk protocol support
both CAP and netatalk can make use of this..
still needs some owrk but it seemd the right tiime to commit it
so other can experiment.
