sctp: fix missing SCTP mailing list address update

The commit 91705c61 ("net: sctp: trivial: update mailing list
address") updated almost all the SCTP mailing list address from

	"lksctp-developers@lists.sourceforge.net"
to
	"linux-sctp@vger.kernel.org"

except for the one in include/linux/sctp.h file. Fix this way trivial
one so that all is updated.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Cc: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>