MFC: r230801

MFC: r230801
jwd@ reported a problem via email to freebsd-fs@ on Aug 25, 2011
under the subject "F_RDLCK lock to FreeBSD NFS fails to R/O target file".
This occurred because the server side NLM always checked for VWRITE
access, irrespective of the type of lock request. This patch
replaces VOP_ACCESS(..VWRITE..) with one appropriate to
the lock operation. It allows unlock and lock cancellation
to be done without a check of VOP_ACCESS(), so that files
can't be left locked indefinitely after the file permissions
have been changed.

git-svn-id: svn://svn.freebsd.org/base/stable/9@231633 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f