Stuck in Searching/Connecting: Resolve the two requests mystery

Related to https://git.jami.net/savoirfairelinux/ring-daemon/issues/227

Reproduce steps

1. device B cut its connectivity
2. device A calls device B (with the connecting lock, cf https://git.jami.net/savoirfairelinux/ring-daemon/issues/243)
3. device A is blocked in "Searching"
4. after a while, device B is back online
5. device A receives 2 ICE response

Expected results

Only one answer should be received (the one from the fallback request)