/*
 * call-seq:
 *   easy.local_port = fixnum or nil                  => fixnum or nil
 *
 * Set the local port that will be used for the following +perform+ calls.
 *
 * Passing +nil+ will return to the default behaviour (no local port
 * preference).
 *
 * This option is ignored if compiled against libcurl < 7.15.2.
 */
static VALUE ruby_curl_easy_local_port_set(VALUE self, VALUE local_port) {