socket-buffer implementations, introduce a return value for MCLGET()
(and m_cljget() that underlies it) to allow the caller to avoid testing
M_EXT itself. Update all callers to use the return value.
With this change, very few network device drivers remain aware of
M_EXT; the primary exceptions lie in mbuf-chain pretty printers for
debugging, and in a few cases, custom mbuf and cluster allocation
implementations.
NB: This is a difficult-to-test change as it touches many drivers for
which I don't have physical devices. Instead we've gone for intensive
review, but further post-commit review would definitely be appreciated
to spot errors where changes could not easily be made mechanically,
but were largely mechanical in nature.
Differential Revision: https://reviews.freebsd.org/D1440
Reviewed by: adrian, bz, gnn
Sponsored by: EMC / Isilon Storage Division
