sctp: fix test for end of loop

Add a list_has_sctp_addr function to simplify loop

Based on a patches by Dan Carpenter and David Miller

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>