procd: mdns: Support txt values with spaces

Properly quote the arguments so that you can register a service with TXT
entries that contains spaces.

Example:
   procd_add_mdns myservice tcp 9999 "key=descriptive text field 1" \
         "another=something equally verbose"

Output before:
$ avahi-browse -r -v _myservice._tcp
_myservice._tcp      local
   hostname = [blah.local]
   address = [192.168.255.74]
   port = [9999]
   txt = ["verbose" "equally" "another=something" "1" "field" "text" "key=descriptive"]

Output now:
$ avahi-browse -r -v _myservice._tcp
_myservice._tcp      local
   hostname = [blah.local]
   address = [192.168.255.74]
   port = [9999]
   txt = ["another=something equally verbose" "key=descriptive text field 1"]

Signed-off-by: Karl Palsson <karlp@etactica.com>
(cherry picked from commit 7a423c389a)

package/system/procd/files/procd.sh

@@ -423,7 +423,7 @@ procd_add_mdns_service() {
 	json_add_int port "$port"
 	[ -n "$1" ] && {
 		json_add_array txt
-		for txt in $@; do json_add_string "" $txt; done
+		for txt in "$@"; do json_add_string "" "$txt"; done
 		json_select ..
 	}
 	json_select ..
@@ -432,7 +432,7 @@ procd_add_mdns_service() {
 procd_add_mdns() {
 	procd_open_data
 	json_add_object "mdns"
-	procd_add_mdns_service $@
+	procd_add_mdns_service "$@"
 	json_close_object
 	procd_close_data
 }