Support for mDNS candidate SDP and resolve mdns if config have option

[varghesepaul]

Webrtc is pushing mDNS support for private IP leak. So if the SDP candidate have mDNS then freeswitch breaking the call saying INCOMPATIBLE_DESTINATION.

mDNS : https://bloggeek.me/psa-mdns-and-local-ice-candidates-are-coming/

Candidate in SDP offer

a=candidate:4096337158 1 udp 2113937151 39330519-b9d7-4d00-9f7d-d1d22137d6de.local 49433 typ host generation 0 network-cost 999
a=candidate:4096337158 2 udp 2113937150 39330519-b9d7-4d00-9f7d-d1d22137d6de.local 55970 typ host generation 0 network-cost 999
a=candidate:842163049 2 udp 1677729534 206.15.76.98 9496 typ srflx raddr 0.0.0.0 rport 0 generation 0 network-cost 999
a=candidate:842163049 1 udp 1677729535 206.15.76.98 1421 typ srflx raddr 0.0.0.0 rport 0 generation 0 network-cost 999

Freeswitch log Error

[DEBUG] switch_core_media.c:6878 AUDIO RTP [sofia/lv_sip/[email protected]] 10.111.21.219 port 17682 -> 39330519-b9d7-4d00-9f7d-d1d22137d6de.local port 49433 codec: 111 ms: 20317393ca-bad4-11e9-9b3d-a72334737892
[DEBUG] switch_core_media.c:6878 AUDIO RTP [sofia/lv_sip/[email protected]] 10.111.21.219 port 17682 -> 39330519-b9d7-4d00-9f7d-d1d22137d6de.local port 49433 codec: 111 ms: 20317393ca-bad4-11e9-9b3d-a72334737892
[DEBUG] switch_rtp.c:4150 Starting timer [soft] 960 bytes per 20ms317393ca-bad4-11e9-9b3d-a72334737892 2019-08-09 14:33:33.717009
[ERR] switch_core_media.c:7567 AUDIO RTP REPORTS ERROR: [Remote Address Error!]317393ca-bad4-11e9-9b3d-a72334737892 2019-08-09 14:33:33.717009
[NOTICE] switch_core_media.c:7568 Hangup sofia/lv_sip/[email protected] [CS_EXECUTE] [INCOMPATIBLE_DESTINATION]

Created a patch, which will try to check if the candidate is an IP address. If it is not IP address, then it will check a new config option ice-resolve-candidate set or not. If the flag is set then will try to resolve the mDNS or just drop the candidate and try the other one.

The new flag option ice-resolve-candidate in switch.conf.xml to resolve the candidate.

Can you please review this PR ?.