net/ipv6: Fix CALIPSO causing GPF with datagram support

net/ipv6: Fix CALIPSO causing GPF with datagram support

[ Upstream commit e3ebdb20fddacded2740a333ff66781e0d28b05c ]

When using CALIPSO with IPPROTO_UDP it is possible to trigger a GPF as the
IP header may have moved.

Also update the payload length after adding the CALIPSO option.

Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>