Add support for receiving and setting flowtype, flowid and RSS bucket
information as part of recvmsg().

This is primarily used for debugging/verification of the various
processing paths in the IP, PCB and driver layers.

Unfortunately the current implementation of the control message path
results in a ~10% or so drop in UDP frame throughput when it's used.

Differential Revision:	https://reviews.freebsd.org/D527
Reviewed by:	grehan


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271293 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f