resolved: also flush /etc/hosts on reload

When we are told to reload our configuration also flush out /etc/hosts
explicitly. This is particularly relevant since we suppress too frequent
reloads, and hence a synchronous way to force a reload is very useful.

src/resolve/resolved-etc-hosts.c

@@ -72,6 +72,7 @@ void etc_hosts_clear(EtcHosts *hosts) {
 void manager_etc_hosts_flush(Manager *m) {
         etc_hosts_clear(&m->etc_hosts);
         m->etc_hosts_stat = (struct stat) {};
+        m->etc_hosts_last = USEC_INFINITY;
 }
 
 static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {

src/resolve/resolved-manager.c

@@ -659,6 +659,7 @@ static int manager_dispatch_reload_signal(sd_event_source *s, const struct signa
         m->unicast_scope = dns_scope_free(m->unicast_scope);
         m->delegates = hashmap_free(m->delegates);
         dns_trust_anchor_flush(&m->trust_anchor);
+        manager_etc_hosts_flush(m);
 
         manager_set_defaults(m);