Handle chained reverse proxies in XFF headers

An X-Forwarded-For header with a single intermediary proxy looks like:

    X-Forwarded-For: $clientip[:$port]

If, however, you're a goofball and like to proxy your proxies (yo dawg!)
it will look like this instead:

    X-Forwarded-For: $clientip[:$port], $proxy1[:$port]

SHIELD now supports the latter as well, and will not stupidly put a
comma-separated value in the Agent IP field.

core/api_v2.go

@@ -1763,7 +1763,7 @@ func (c *Core) v2API() *route.Router {
 			return
 		}
 
-		peer := regexp.MustCompile(`:\d+$`).ReplaceAllString(r.Req.Header.Get("X-Forwarded-For"), "")
+		peer := regexp.MustCompile(`[,:].*`).ReplaceAllString(r.Req.Header.Get("X-Forwarded-For"), "")
 		if peer == "" {
 			peer = regexp.MustCompile(`:\d+$`).ReplaceAllString(r.Req.RemoteAddr, "")
 			if peer == "" {