For vunref(), try to upgrade the vnode lock if the function was called with the vnode shared-locked.  If upgrade succeeded, the inactivation can be done immediately, instead of being postponed.
For vunref(), try to upgrade the vnode lock if the function was called
with the vnode shared-locked.  If upgrade succeeded, the inactivation
can be done immediately, instead of being postponed.

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Approved by:	re (glebius)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase