socket: bump listen() backlog to INT_MAX everywhere

This is a rework of #24764 by Cristian Rodríguez
<crodriguez@owncloud.com>, which stalled.

Instead of assigning -1 we'll use a macro defined to INT_MAX however.

src/shared/socket-netlink.c

@@ -180,7 +180,7 @@ int make_socket_fd(int log_level, const char* address, int type, int flags) {
 
         a.type = type;
 
-        fd = socket_address_listen(&a, type | flags, SOMAXCONN, SOCKET_ADDRESS_DEFAULT,
+        fd = socket_address_listen(&a, type | flags, SOMAXCONN_DELUXE, SOCKET_ADDRESS_DEFAULT,
                                    NULL, false, false, false, 0755, 0644, NULL);
         if (fd < 0 || log_get_max_level() >= log_level) {
                 _cleanup_free_ char *p = NULL;

src/shared/varlink.c

@@ -2750,7 +2750,7 @@ int varlink_server_listen_address(VarlinkServer *s, const char *address, mode_t
                         return r;
         }
 
-        if (listen(fd, SOMAXCONN) < 0)
+        if (listen(fd, SOMAXCONN_DELUXE) < 0)
                 return -errno;
 
         r = varlink_server_create_listen_fd_socket(s, fd, &ss);