net: ipvs: sctp: add missing verdict assignments in sctp_conn_schedule

If skb_header_pointer() fails, we need to assign a verdict, that is
NF_DROP in this case, otherwise, we would leave the verdict from
conn_schedule() uninitialized when returning.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>