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

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

Reported-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>