Bug - Heartbeat log message does not consider the value of the "HeartbeatPeriod" value.

The problem is in the file /feature/stats/geoip_stats.c, at the fonction format_client_stats_heartbeat(). The variable n_hours is hardcoded to 6 hours, which is the default value. Here is the changes I made to the fonction. I take the opportunity to do a little bit of refactoring. I did not know how to compile the project and test it, but I'm sure you will understand what I'm trying to do.

To fix this issue, n_hours, now renamed n_heartbeat_period, need to take the value of the option->HeartbeatPeriod, which is in seconds.

[- Line 1207 : const int n_hours = 6; -]  
[+ Line 1207 : const int n_heartbeat_period = option->HeartbeatPeriod; +]  
[- Line 1211 : unsigned cutoff = (unsigned)( (now-n_hours*3600)/60 ); -]  
[+ Line 1211 : unsigned cutoff = (unsigned)( (now-n_heartbeat_period)/60 ); +]  
[- Line 1228 : nhours, -]  
[+ Line 1228 : n_heartbeat_period +]

The variable out could also be renamed msg.

[- Line 1208 : char *out = NULL; -]  
[+ Line 1208 : char *msg = NULL; +]  
[- Line 1226 : tor_asprintf(&out, "Heartbeat: " -]  
[+ Line 1226 : tor_asprintf(&msg, "Heartbeat: " +]  
[- Line 1231 : return out; -]  
[+ Line 1231 : return msg; +]  

A clientmap_entry_t is a client, so why not call it that way to make it more clear instead of ent.

[- Line 1210 : clientmap_entry_t **ent; -]  
[+ Line 1210 : clientmap_entry_t **client; +]  
[- Line 1217 : HT_FOREACH(ent, clientmap, &client_history) { -]  
[+ Line 1217 : HT_FOREACH(client, clientmap, &client_history) { +]  
[- Line 1219 : if ((*ent)->action != GEOIP_CLIENT_CONNECT) -]  
[+ Line 1219 : if ((*client)->action != GEOIP_CLIENT_CONNECT) +]  
[- Line 1221 : if ((*ent)->last_seen_in_minutes < cutoff) -]  
[+ Line 1221 : if ((*client)->last_seen_in_minutes < cutoff) +]  

Prettier msg :simple_smile:

[- Line 1226 : tor_asprintf(&out, "Heartbeat: " -]  
[- Line 1227 :              "In the last %d hours, I have seen %d unique clients.", -]  
[- Line 1228 :              n_hours, -]  
[- Line 1229 :              n_clients); -]  
[+ Line 1226 : tor_asprintf(&msg, "Heartbeat: In the last %d hour%s, I have seen %u unique client%s.", +]  
[+ Line 1227 :              n_heartbeat_period*60*60, +]  
[+ Line 1228 :	            n_heartbeat_period >= 60*60*2 ? "s" : "", +]  
[+ Line 1229 :              n_clients, +]  
[+ Line 1230 :              n_clients > 1 ? "s" : ""); +]  

Message to the moderator about my GitLab Flavored Markdown skills : My last issue is horrible and this one will certainly be, because I can't validate the formating before submitting it! I'm so sorry.