rend_handshake: retry up to `hs_service_max_rdv_failures`.

13:00 <+nickm> second question is about when services connect to a rendezvous 
               point.  If their first attempt to connect to a rend point fails, 
               does the service retry, or does it assume the client will send 
               another introduce message?
13:01 <+dgoulet> it does retry and there is a cap on that... which might be 
                 even a consensus param, give me a sec to check
13:01 <+dgoulet>     "hs_service_max_rdv_failures" -- This parameter determines 
                 the
13:01 <+dgoulet>     maximum number of rendezvous attempt an HS service can 
                 make per
13:01 <+dgoulet>     introduction.
13:01 <+dgoulet>     Min 1. Max 10. Default 2.
13:01 <+dgoulet>     First-appeared: 0.3.3.0-alpha.
13:01 <+nickm> ack
13:01 <+dgoulet> which FYI, dirauth are voting this at the moment: 
                 "hs_service_max_rdv_failures=1"
13:02 <+dgoulet> (we brought it down during the DoS)