ocfs2: Create locks at initially requested level

If we have not yet created a cluster lock, ocfs2_cluster_lock() will
first create it at NLMODE, and then convert the lock to either PRMODE or
EXMODE (whichever is requested).

Change ocfs2_cluster_lock() to just create the lock at the initially
requested level. ocfs2_locking_ast() handles this case fine, so the only
update required was in setup of locking state. This should reduce the number
of network messages required for a new lock by one, providing an incremental
performance enhancement.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>