Have BIO_get_conn_int_port use BIO_ctrl instead BIO_int_ctrl

BIO_int_ctrl isn't made for the purpose BIO_get_conn_int_port used it
for.

This also changes BIO_C_GET_CONNECT to actually return the port
instead of assigning it to a pointer that was never returned back to
the caller.

Reviewed-by: Rich Salz <rsalz@openssl.org>