UPSTREAM: ipv6: raw: Deduct extension header length in rawv6_push_pending_frames

commit cb3e9864cdbe35ff6378966660edbcbac955fe17 upstream.

The total cork length created by ip6_append_data includes extension
headers, so we must exclude them when comparing them against the
IPV6_CHECKSUM offset which does not include extension headers.

Reported-by: Kyle Zeng <zengyhkyle@gmail.com>
Fixes: 357b40a1 ("[IPV6]: IPV6_CHECKSUM socket option can corrupt kernel memory")
Change-Id: I73cf556998cab122229e1a361d186925775aad61
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 35ed8ba485544a31a4ab9b92a1c68e406ab66a47)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Signed-off-by: Jprimero15 <jprimero155@gmail.com>