bnx2x: fix AFEX memory overflow

There are 2 different (related) flows in the slowpath configuration
that utilize the same pointer and cast it to different structs;
This is obviously incorrect as the intended allocated memory is that
of the smaller struct, possibly causing the flow utilizing the larger
struct to corrupt other slowpath configuration.

Since both flows are exclusive, set the allocated memory to be a union
of both structs.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>