mod_s2s_keepalive: Fix response handler (thanks Ge0rG) So there are no 'iq-{result,error}/host' events, mod_iq only fires events for result stanzas that include the full 'id' attr. This fixes it by hooking the stanza router event.

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summary: Log a message once per minute
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This module sends `-- MARK --` to the log once per minute. This may be
useful to give a sense of how busy the server is or see that logging and
timers are still working.