[IPSEC] beet: Fix extension header support on output

The beet output function completely kills any extension headers by replacing
them with the IPv6 header.  This is because it essentially ignores the
result of ip6_find_1stfragopt by simply acting as if there aren't any
extension headers.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>