LU-13503 mdc: allow setting max_mod_rpcs_in_flight larger

LU-13503 mdc: allow setting max_mod_rpcs_in_flight larger

Allow setting mdc.*.max_mod_rpcs_in_flight > mdc.*.max_rpcs_in_flight
by increasing the latter value, rather than returning an error and
telling the user to do that.  This matches the similar behavior if
mdc.*.max_rpcs_in_flight is reduced lower than max_mod_rpcs_in_flight.

If there are multiple MDTs, the "mdc.*.max_mod_rpcs_in_flight" param
may be set from e.g. the MDT0000 config log before MDT0001 is fully
configured, catching MDT0001 with ocd_maxmodrpcs = 0 before the OCD
from the MDT has been filled in, and incorrectly trigger an error.
If seen during setup, allow ocd_maxmodrpcs = (max_rpcs_in_flight - 1),
since this will be fixed up later if mdc.*.max_rpcs_in_flight is set
smaller in the config log (if set larger it doesn't matter).

Test-Parameters: env=ONLY=90 testlist=conf-sanity

This patch is back-ported from the following one:
Lustre-commit: 6d314902e6d19229379577aab60d4b20a5b4d2ea
Lustre-change: https://review.whamcloud.com/38455

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Change-Id: I4b20163e9e212db451738169ebdc361ab8c1c15e
Reviewed-on: https://review.whamcloud.com/38893
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>