Apply the change from r272770 to if_ipsec(4) interface.

It is guaranteed that if_ipsec(4) interface is used only for tunnel
mode IPsec, i.e. decrypted and decapsultaed packet has its own IP header.
Thus we can consider it as new packet and clear the protocols flags.
This allows ICMP/ICMPv6 properly handle errors that may cause this packet.

PR: 228108
MFC after: 1 week