LU-8582 target: send error reply on wrong opcode

LU-8582 target: send error reply on wrong opcode

Unknown opcode does not necessarily means insane client. A new client
might send RPCs with new opcodes to an old server. The client might
desperately stuck there waiting for a reply. So, send an error back
when RPC has a wrong opcode.

This patch returns the EOPNOTSUPP to client instead of block. ENOTSUPP
is not used here since strerror() does not understand ENOTSUPP.

OBD_FAIL_OST_OPCODE=0x253 is added for fault injection test of opcode.
To test whether an invalid opcode is handled properly on OST, use the
following command:

lctl set_param fail_val=${opcode} fail_loc=0x253

Change-Id: I46ca62bc532b92368e06a4f883b102c7186c453c
Signed-off-by: Li Xi <lixi@ddn.com>
Reviewed-on: https://review.whamcloud.com/47761
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>