socket: Set SO_REUSEPORT before bind()

bind() fails if it is called before setting SO_REUSEPORT and another
process is already binded to the same addess.

A new reuse_port option has been introduced to socket_address_listen()
to set the option as part of socket initialization.

src/basic/socket-util.h

@@ -80,6 +80,7 @@ int socket_address_listen(
                 int backlog,
                 SocketAddressBindIPv6Only only,
                 const char *bind_to_device,
+                bool reuse_port,
                 bool free_bind,
                 bool transparent,
                 mode_t directory_mode,