unix-socket: don't try to change permissions on BSD

On BSD using fchmod on a socket is not supported and will result
in EINVAL.

src/unix-manager.c

@@ -167,9 +167,10 @@ int UnixNew(UnixCommand * this)
     }
     this->select_max = this->socket + 1;
 
+#if !(defined OS_FREEBSD || defined __OpenBSD__)
     /* Set file mode: will not fully work on most system, the group
-     * permission is not changed on some Linux and *BSD won't do the
-     * chmod. */
+     * permission is not changed on some Linux. *BSD won't do the
+     * chmod: it returns EINVAL when calling fchmod on sockets. */
     ret = fchmod(this->socket, S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP);
     if (ret == -1) {
         int err = errno;
@@ -178,6 +179,7 @@ int UnixNew(UnixCommand * this)
                      strerror(err),
                      err);
     }
+#endif
     /* set reuse option */
     ret = setsockopt(this->socket, SOL_SOCKET, SO_REUSEADDR,
                      (char *) &on, sizeof(on));