Pull request: * all: allow multiple hosts in reverse lookups

Merge in DNS/adguard-home from 2269-multiple-hosts to master

For #2269.

Squashed commit of the following:

commit f8ae452540b106f2d5b130b8edb08c4e76b003f4
Merge: 8dd06f7cc 3e1f92225
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Nov 6 17:28:12 2020 +0300

    Merge branch 'master' into 2269-multiple-hosts

commit 8dd06f7cca27ec32a4690e2673603b166f82af0a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Nov 5 20:28:33 2020 +0300

    * all: allow multiple hosts in reverse lookups

internal/home/clients.go

@@ -606,22 +606,25 @@ func (clients *clientsContainer) rmHosts(source clientSource) int {
 	return n
 }
 
-// Fill clients array from system hosts-file
+// addFromHostsFile fills the clients hosts list from the system's hosts files.
 func (clients *clientsContainer) addFromHostsFile() {
 	hosts := clients.autoHosts.List()
 
 	clients.lock.Lock()
 	defer clients.lock.Unlock()
+
 	_ = clients.rmHosts(ClientSourceHostsFile)
 
 	n := 0
-	for ip, name := range hosts {
-		ok, err := clients.addHost(ip, name, ClientSourceHostsFile)
-		if err != nil {
-			log.Debug("Clients: %s", err)
-		}
-		if ok {
-			n++
+	for ip, names := range hosts {
+		for _, name := range names {
+			ok, err := clients.addHost(ip, name, ClientSourceHostsFile)
+			if err != nil {
+				log.Debug("Clients: %s", err)
+			}
+			if ok {
+				n++
+			}
 		}
 	}