Fix: if externip is not set fallback to ipaddress of incoming interface. Remove deprecation from externip parameter. This will restore previous behaviour but still provide NAT behaviour needed for PBX on sepeperate host behind natted firewall. (Reported by Dan / Pavel / Ian)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5616 43c1dc8c-776e-4df2-8ef1-6e829299be21