mod_s2s_keepalive: Use timestamp as iq @id RFC 6120 implies that the id attribute must be unique within a stream. This should fix problems with remote servers that enforce uniqueness and don't answer duplicated ids. If it doesn't do that, then at least you can get a guesstimate at round-trip time from the difference between the result iq stanza and the timestamp it was logged without having to go look for when it was sent, or needing to keep state.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```