cnic: Fine-tune CID memory space calculation.

The current code makes assumptions about the CID (context ID) memory
space and starting CID that may not be always correct when firmware
changes.  In particular, BNX2_ISCSI_START_CID may not always be fixed.
We now calculate cp->max_cid_space and cp->iscsi_start_cid dynamically
instead of using fixed constants.  The unused cp->max_iscsi_conn is also
eliminated.

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