gfs2: Rename GLF_REPLY_PENDING to GLF_HAVE_REPLY

The GLF_REPLY_PENDING flag indicates to glock_work_func() that in
response to a locking request, DLM has sent a reply that needs to be
processed.  A flag with that name could as well indicate that we are
waiting on a reply from DLM, however.  To disambiguate these two cases,
rename the flag to GLF_HAVE_REPLY.

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