bonding: 3ad: remove bond_3ad_rx_indication's length argument

Since the received lacpdu is accessed via skb_header_pointer() in
bond_3ad_lacpdu_recv() we no longer need to check for skb->len's length.
If the returned lacpdu pointer is not null that should be enough.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>