gfs2: Fix missed wakeups in find_insert_glock

Mark Syms has reported seeing tasks that are stuck waiting in
find_insert_glock.  It turns out that struct lm_lockname contains four padding
bytes on 64-bit architectures that function glock_waitqueue doesn't skip when
hashing the glock name.  As a result, we can end up waking up the wrong
waitqueue, and the waiting tasks may be stuck forever.

Fix that by using ht_parms.key_len instead of sizeof(struct lm_lockname) for
the key length.

Reported-by: Mark Syms <mark.syms@citrix.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>