base-files: failsafe: Remove the VLAN modifier from interface name

Some interfaces have a VLAN modifier like :t in lan1:t, this modifier
should be removed from the interface before calling preinit_ip_config().

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 790561d510)

package/base-files/files/lib/preinit/10_indicate_preinit

@@ -97,6 +97,8 @@ preinit_config_board() {
 	else
 		# trim any vlan ids
 		ifname=${ifname%\.*}
+		# trim any vlan modifiers like :t
+		ifname=${ifname%\:*}
 	fi
 
 	pi_ifname=$ifname