Update endpoint/grandstream/gxphd/template_data.json

The original value of line 22:
                "default_value":"{ x+ | *x+ | *xx*x+ }",
does not provision the GXP2124 correctly over tftp. The plus signs disappear, causing the phone to have no valid dial plan. Per Grandstream's recommendation, and personal success in changing it, I recommend modifying the provisioning script to:
              "default_value":"{ x%2B | *x%2B | *xx*x%2B }",

I've verified this provisions the default dial plan correctly on the GXP2124.

For further information, visit this thread:

http://forums.grandstream.com/forums/index.php?topic=12752.0

Supposedly, a fix was put in place, but I have a new clean install fully updated, and the '+' still doesn't make it into the dialplan. Modifying the template fixed the problem for me.

Thank you!