dnsmasq: Fix hosts file format when MAC address is not specified

An entry like this in /etc/config/dhcp:

    config 'host'
        option 'name' 'pc2'
        option 'ip' '192.168.100.56'
        option 'dns' '1'

results in a /tmp/hosts/dhcp entry that looks like this:

    192.168.100.56 .lan

Obviously it should say "pc2.lan".

This happens because $name is set to "" in order to support the MAC-less
syntax: "--dhcp-host=lap,192.168.0.199".  Fix this by reordering the
operations.  Also, refuse to add a DNS entry if the hostname or IP is
missing.

Fixes #17683

Reported-by: Kostas Papadopoulos <kpapad75@travelguide.gr>
Signed-off-by: Kevin Cernekee <cernekee@gmail.com>

Backport of r42319

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42389 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/network/services/dnsmasq/files/dnsmasq.init

@@ -293,6 +293,11 @@ dhcp_host_add() {
 	config_get ip "$cfg" ip
 	[ -n "$ip" -o -n "$name" ] || return 0
 
+	config_get_bool dns "$cfg" dns 0
+	[ "$dns" = "1" -a -n "$ip" -a -n "$name" ] && {
+		echo "$ip $name${DOMAIN:+.$DOMAIN}" >> $HOSTFILE
+	}
+
 	config_get mac "$cfg" mac
 	[ -z "$mac" ] && {
 		[ -n "$name" ] || return 0
@@ -309,11 +314,6 @@ dhcp_host_add() {
 	[ "$broadcast" = "0" ] && broadcast=
 
 	xappend "--dhcp-host=$macs${networkid:+,net:$networkid}${broadcast:+,set:needs-broadcast}${tag:+,set:$tag}${ip:+,$ip}${name:+,$name}"
-
-	config_get_bool dns "$cfg" dns 0
-	[ "$dns" = "1" ] && {
-		echo "$ip $name${DOMAIN:+.$DOMAIN}" >> $HOSTFILE
-	}
 }
 
 dhcp_tag_add() {