sctp: Correct byte order of access to skb->{network, transport}_header

Corrects an byte order conflict introduced by
158874ca
("sctp: Correct access to skb->{network, transport}_header").
The values in question are host byte order.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>