For consistency with the shared header file (and to avoid confusion
with mbufs normally called *m in one place), rename the function
arguments to "mem".

This is a non-functional change.

Reviewed by:	gnn, eric.joyner intel.com
MFC after:	3 days
- Use NULL instead of 0 for fpcurthread.
- Note the quirk with the interrupt enabled state of the dna handler.
- Use just panic() instead of printf() and panic().  Print tid instead
  of pid, the fpu state is per-thread.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week