bnxt_en: Reserve completion rings and MSIX for bnxt_re RDMA driver.

Add additional logic to reserve completion rings for the bnxt_re driver
when it requests MSIX vectors.  The function bnxt_cp_rings_in_use()
will return the total number of completion rings used by both drivers
that need to be reserved.  If the network interface in up, we will
close and open the NIC to reserve the new set of completion rings and
re-initialize the vectors.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>