nvme-fabrics: set sqe.command_id in core not transports

Currently, core.c sets command_id only on rd/wr commands, leaving it to
the transport to set it again to ensure the request had a command id.

Move location of set in core so applies to all commands.
Remove transport sets.

Signed-off-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Jay Freyensee <james_p_freyensee@linux.intel.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>