gfs2: Rename GLF_FROZEN to GLF_HAVE_FROZEN_REPLY

The GLF_FROZEN flag indicates that a reply to a DLM locking request has
been received, but should not be processed at this time.  To clarify
that meaning, rename the flag to GLF_HAVE_FROZEN_REPLY.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>