MT#9205 add kamailio.proxy.nathelper_dbro config

Defaul is "no". This will be "yes" on CARRIER in order to
activate the use of a read-only connection using LOCAL_URL

Change-Id: Ie8bd5f2e44f79610b6b3040f19a6b5ebf66a5a20
cfg-schema dump: snapshot Thu Oct 02 01:13:12 +0200 2014