bnxt_en: Change IRQ assignment for RDMA driver.

In the current code, the range of MSIX vectors allocated for the RDMA
driver is disjoint from the network driver.  This creates a problem
for the new firmware ring reservation scheme.  The new scheme requires
the reserved completion rings/MSIX vectors to be in a contiguous
range.

Change the logic to allocate RDMA MSIX vectors to be contiguous with
the vectors used by bnxt_en on new firmware using the new scheme.
The new function bnxt_get_num_msix() calculates the exact number of
vectors needed by both drivers.

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