sctp: change return type of sctp_get_port_local

Currently sctp_get_port_local() returns a long
which is either 0,1 or a pointer casted to long.
It's neither of the callers use the return value since
commit 62208f12

 ("net: sctp: simplify sctp_get_port").
Now two callers are sctp_get_port and sctp_do_bind,
they actually assumend a casted to an int was the same as
a pointer casted to a long, and they don't save the return
value just check whether it is zero or non-zero, so
it would better change return type from long to int for
sctp_get_port_local.

Signed-off-by: Mao Wenan <maowenan@huawei.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>