ipsec: Don't update the pmtu on ICMPV6_DEST_UNREACH

Currently we update the pmtu in the IPsec protocol error handlers
if icmpv6 message type is either ICMPV6_DEST_UNREACH or
ICMPV6_PKT_TOOBIG. Updating the pmtu on ICMPV6_DEST_UNREACH
is wrong in any case, it causes strangely fragmented packets.
Only ICMPV6_PKT_TOOBIG signalizes pmtu discovery, so remove the
ICMPV6_DEST_UNREACH check in the IPsec protocol error handlers.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --cc net/ipv6/ah6.c
Simple merge

diff --cc net/ipv6/esp6.c
Simple merge

diff --cc net/ipv6/ipcomp6.c
Simple merge