IPv6 can be build as a module, so we need mechanism to access
the address family dependent callback functions properly.
Therefore we introduce xfrm_input_afinfo, similar to that
what we have for the address family dependent part of
policies and states.
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

IPsec vti_rcv needs to remind the tunnel pointer to
check it later at the vti_rcv_cb callback. So add
this pointer to the IPsec common buffer, initialize
it and check it to avoid transport state matching of
a tunneled packet.
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

This patch add an IPsec protocol multiplexer. With this
it is possible to add alternative protocol handlers as
needed for IPsec virtual tunnel interfaces.
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>