lantiq: fix logic error in dsl board.d code

Starting with r47755 the pppoe wan interface section isn't any longer added to
the network config on firstboot, using the default configuration. Since the
commit message does not mention such a change, I assume that this wasn't
intentionally.

Signed-off-by: Mathias Kresin <openwrt@kresin.me>

SVN-Revision: 47793

target/linux/lantiq/base-files/etc/board.d/02_network

@@ -130,7 +130,7 @@ VGV7510KW22)
 
 esac
 
-if [ -z "$(ls /lib/modules/`uname -r`/ltq_atm*)" ]; then
+if [ -n "$(ls /lib/modules/`uname -r`/ltq_atm*)" ]; then
 	ucidef_add_atm_bridge "$vpi" "$vci" "$encaps" "$payload"
 	ucidef_set_interface_wan "nas0" "pppoe"
 fi