We cannot use net.ReadFrom on darwin because a) net.ReadFrom and
net.ReadFromIP unconditionally try to strip off ipv4 header due to
and c) icmp.ListenPacket calls ipv4.PacketConn internally.

Instead, we use ipv4.PacketConn.ReadFrom that calls net.ReadMsgIP
internally to prevent icmp.ReadFrom from returning corrupted ICMP
message.

Fixes #9395.

Change-Id: I269f3724de72bf37eb26921c251c2acb1c720fa3