Revert "docs: features/multidomain.rst: use gluon-reload instead of reboot (#1888)"

This reverts commit 4e070312.

The recommendation is not sufficient at this time, so revert it.

See #1898 for further discussion.

docs/features/multidomain.rst

@@ -94,7 +94,7 @@ Switching the domain
 
     uci set gluon.core.domain="newdomaincode"
     gluon-reconfigure
-    gluon-reload
+    reboot
 
 **via config mode:**