Fix a bug in r265255: only return NULL if the requested map wasn't found.

Submitted by:	Luke Chang-Hsien Tsai <luke.tw@gmail.com>
MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@270506 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Fix bug that, assuming a/ is a root of NFS filesystem mounted on autofs,
prevented "mv a/from a/to" from working, while "cd a && mv from to" was ok.

PR:		192948
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@270507 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Restore the correct value when disabling probes. Otherwise the instrumented
tracepoints would continue to generate traps, which would be ignored but
could consume noticeable amounts of CPU if, say, all functions in the kernel
were instrumented.

X-MFC-With:	r270067


git-svn-id: svn+ssh://svn.freebsd.org/base/head@270508 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f