RDMA/cxgb3: Enforce required firmware

The cxgb3 NIC driver can handle more firmware versions than iw_cxgb3,
and since commit 8207befa

 ("cxgb3: untie strict FW matching") cxgb3
will load with firmware versions that iw_cxgb3 can't handle.  The FW
major number indicates a specific interface between the FW and
iw_cxgb3.  Thus if the major number of the running firmware does not
match the required version compiled into iw_cxgb3, then iw_cxgb3 must
not register that device.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>