return a pointer to a void. The send_thread() and disk_thread()
funtions; however, do not have a return value because they run for
the duration of the daemon's lifetime. This causes gcc to barf when
running with -O3. Make these functions return a null pointer to quiet it.
PR: bin/124342
Submitted by: Garrett Cooper <gcooper@FreeBSD.org> (minus his comments)
MFC after: 1 week