Replace local copy-and-paste implementations of printmbuf() in several
device drivers with calls to the centralised m_print() implementation.
While the formatting and output details differ a little, the content
is essentially the same, and it is unlikely anyone has used this
debugging output in some time.

This change reduces awareness of mbuf cluster allocation (and,
especially, the M_EXT flag) outside of the mbuf allocator, which will
make it easier to refine the external storage mechanism without
disrupting drivers in the future.

Style bugs are preserved.

Reviewed by:	bz, glebius
MFC after:	3 days
Sponsored by:	EMC / Isilon Storage Division