rxrpc: Don't pick values out of the wire header when setting up security

[ Upstream commit a1c9af4d ]

Don't pick values out of the wire header in rxkad when setting up DATA
packet security, but rather use other sources.  This makes it easier to get
rid of txb->wire.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>