be2net: fix payload_len value for GET_MAC_LIST cmd req

The buffer size for a FW cmd request must be big enough to fit the response,
else the cmd fails. For GET_MAC_LIST cmd, though the memory allocated for
the cmd is big enough to fit the response, the payload_len value in the
WRB hdr is being set to the request length only.
Fix this for GET_MAC_LIST cmd.

Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>