Remove local LAN address ICE candidates

ICE candidates can contain local LAN addresses as well as external addresses. For example, here's a redacted transcript from the Snowflake JS proxy:

a=candidate:4077567720 1 udp 2122260223 192.168.1.5 51282 typ host generation 0
a=candidate:8564102000 1 udp 1686052607 X.X.X.X 51282 typ srflx raddr 192.168.1.5 rport 51282 generation 0
a=candidate:3179889176 1 tcp 1518280447 192.168.1.5 52256 typ host tcptype passive generation 0

If it's possible, we should filter them out to prevent revealing more information than necessary. Serene and I guessed that they are only there for the case when both peers are in the same local network, but we're not sure about that.

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