[PFKEY]: Sending an SADB_GET responds with an SADB_GET

From: Charles Hardin <chardin@2wire.com>

Kernel needs to respond to an SADB_GET with the same message type to
conform to the RFC 2367 Section 3.1.5

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>