dnsmasq: fix uci-defaults script to exit 0 so it is cleaned up

A file, package/network/services/dnsmasq/files/50-dnsmasq-migrate-resolv-conf-auto.sh,
was added in commit 6a28552120, but it
does not exit in a way that tells the uci-defaults mechanism that it
succeeded, and so it is not cleaned up after running successfully. Add
an exit 0 to the end to correct that.

Signed-off-by: Russell Senior <russell@personaltelco.net>

package/network/services/dnsmasq/files/50-dnsmasq-migrate-resolv-conf-auto.sh

@@ -4,3 +4,5 @@
 	uci set dhcp.@dnsmasq[0].resolvfile="/tmp/resolv.conf.d/resolv.conf.auto"
 	uci commit dhcp
 }
+
+exit 0