Add 'default' runlevel to x-ui service in Alpine (#3854)

it should be 'default' runlevel when add x-ui service to openrc, default is 'sysinit' runlevel. 'sysinit' runlevel is unnecessary,maybe.
if not, there is an error when call to function 'check_enabled()' as command 'grep default -c' can`t print 'default' runlevel.

check_enabled() {
    if [[ $release == "alpine" ]]; then
        if [[ $(rc-update show | grep -F 'x-ui' | grep default -c) == 1 ]]; then
            return 0
        else
            return 1
        fi

x-ui.sh

@@ -431,7 +431,7 @@ status() {
 
 enable() {
     if [[ $release == "alpine" ]]; then
-        rc-update add x-ui
+        rc-update add x-ui default
     else
         systemctl enable x-ui
     fi