IPVS: Use correct lock in SCTP module

Use sctp_app_lock instead of tcp_app_lock in the SCTP protocol module.

This appears to be a typo introduced by the netns changes.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Hans Schillstrom <hans.schillstrom@ericsson.com>