Satisfy awk(1) on FreeBSD

According to the manual it should be possible to use the {n} notation in
regular expressions but for some reason it doesn't work here.

varnishreload

@@ -111,7 +111,7 @@ vcl_active_file() {
 }
 
 vcl_reload_match() {
-	awk '$1 == "available" && $NF ~ /^reload_[0-9]{8}_[0-9]{6}$/'" {$1}"
+	awk '$1 == "available" && $NF ~ /^reload_[0-9]+_[0-9]+$/'" {$1}"
 }
 
 vcl_reload_count() {