qed: Don't waste SBs unused by RoCE

When RoCE is enabled on a given L2 interface, the interrupt lines
are divided equally between L2 and RoCE -
But in case number of lines needed for RoCE is limited by number
of available CNQs, we can utilize the additional lines for L2.

Signed-off-by: Yuval Mintz <Yuval.Mintz@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>