- 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


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271747 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f