net: in the first call to neigh_seq_next, call neigh_get_first, not neigh_get_idx.

neigh_seq_next won't be called both with *pos > 0 && v ==
SEQ_START_TOKEN, so there's no point calling neigh_get_idx when we're
on the start token, just call neigh_get_first directly.

Signed-off-by: Chris Larson <clarson@mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>