LU-14124 target: set OBD_MD_FLGRANT in read's reply

LU-14124 target: set OBD_MD_FLGRANT in read's reply

If tgt_grant_shrink() decides to not shrink grants - a client is
supposed to restore its cl_grant_avail in osc_update_grant(). In case
of read OBD_MD_FLGRANT is not set on reply's body->oa.o_valid, so
osc_update_grant() misses the cl_grant_avail update. As result server
keeps thinking that client has a lot of grants while a client thinks
that it is missing grants badly. That may lead to performance
degradation.

A test to illustrate the issue is included.

Lustre-change: https://review.whamcloud.com/43375
Lustre-commit: 4894683342d77964daeded9fbc608fc46aa479ee

Change-Id: Ibe7ce0af5701226c8be3ae3f9ad57c354791fa0f
HPE-bug-id: LUS-9943
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46468
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>