rstp: Fix the empty bridge name issue

network_get_device will extract "l3_device" value from
interface's netifd attribute. But when LAN interface is
set to dhcp proto, l3_device is not set. Hence we use
network_get_physdev to get "device" field, which is present
for either dhcp or non-dhcp proto.

Signed-off-by: Tian Yang <quic_tiany@quicinc.com>
Change-Id: Ia44a11100bb6547c59cffcc71ca96e647c1c0295

rstp/files/etc/init.d/rstp

@@ -183,15 +183,14 @@ board_recover() {
 __brctl_stp_on_or_off() {
 	local config="$1"
 	local on_or_off="$2"
-	local type br_device br_ifname
+	local type br
 
 	config_get type "$config" type
 	[ -z "$type" -o ! "$type" = "bridge" ] && return
 
-	br_device="$config"
-	network_get_device br_ifname $br_device
+	network_get_physdev br $1
 
-	brctl stp $br_ifname $on_or_off
+	brctl stp $br $on_or_off
 	sleep 1
 }