LU-2951 mdt: Increase bc_req_max_size for MDS_REQUEST_PORTAL

Large EA tests triggered error messages like this on MDSs:

  10:38:21:LNetError: 3022:0:(lib-ptl.c:190:lnet_try_match_md())
  Matching packet from 12345-10.10.17.9@tcp, match 1429230968490588
  length 65928 too big: 117674 left, 49386 allowed

These were the REINT_SETXATTR requests carrying large EA values.  They
were dropped because the MDSs did not expect request buffers larger
than 49386 bytes.  This patch increases bc_req_max_size (and
bc_rep_max_size) for MDS_REQUEST_PORTAL (and MDS_REPLY_PORTAL) to
accommodate REINT_SETXATTR requests (and MDS_GETXATTR replies) with
255-byte names and 65536-byte values (or 65536-byte lists of EA
names).

Signed-off-by: Li Wei <wei.g.li@intel.com>
Signed-off-by: Sergey Cheremencev <Sergey_Cheremencev@xyratex.com>
Change-Id: Id33555ee6b793627288766672333c2608dbdb1e5
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/610
Tested-by: Jenkins
Reviewed-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Reviewed-by: Cheng Shao <cheng_shao@xyratex.com>
Tested-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>