gfs2: Further sanitize lock_dlm.c

The gl_req field and GLF_BLOCKING flag are only relevant to gdlm_lock(),
its callback gdlm_ast(), and their helpers, so set and clear them inside
lock_dlm.c.

Also, the LM_FLAG_ANY flag is relevant to gdlm_lock(), but do_xmote()
doesn't pass that flag down to gdlm_lock() as it should.  Fix that by
passing down all the flags.

In addition, document the effect of the LM_FLAG_ANY flag on locks held
in EX mode locally.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Andrew Price <anprice@redhat.com>