Disable recursion for the process spinlock.

Tested by:	pho
Discussed with:	jhb
Sponsored by:	The FreeBSD Foundation
MFC after:	1 month


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275372 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f