NFS: make sure lock/nolock overriding local_lock mount option

Currently, mount option lock/nolock and local_lock option
may override NFS_MOUNT_LOCAL_FLOCK NFS_MOUNT_LOCAL_FCNTL flags
when passing in different order:

mount -o vers=3,local_lock=all,lock:
	local_lock=none

mount -o vers=3,lock,local_lock=all:
	local_lock=all

This patch will let lock/nolock override local_lock option
as nfs(5) suggested.

Signed-off-by: Chen Hanxiao <chenhx.fnst@fujitsu.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>