bnx2x: Count number of possible FCoE interfaces

Commit 0eb43b4b
"bnx2x, bnx2fc: Use per port max exchange resources" has changed the number
of available FCoE exchanges, even in scenarios when some of the functions has
no FCoE support; This needlessly degraded the available resources.

Remedy this by calculating the maximal number of functions that may actually
utilize said connection.

Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
CC: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>