bnx2x: credit-leakage fixup on vlan_mac_del_all

Upon insertion of elements into the execution queue, it is validated
that there are enough credits to support additional vlan-macs,
and the credits are consumed. However, when removing a pending
command in `bnx2x_vland_mac_del_all' the consumed credits are not
released, which might cause leakage and eventually the inability to
add new vlan-macs in certain scenarios.

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>