xfrm: Add SA to hardware at the end of xfrm_state_construct()

Current code configures the hardware with a new SA before the state has been
fully initialized. During this time interval, an incoming ESP packet can cause
a crash due to a NULL dereference. More specifically, xfrm_input() considers
the packet as valid, and yet, anti-replay mechanism is not initialized.

Move hardware configuration to the end of xfrm_state_construct(), and mark
the state as valid once the SA is fully initialized.

Fixes: d77e38e6

 ("xfrm: Add an IPsec hardware offloading API")
Signed-off-by: Aviad Yehezkel <aviadye@mellnaox.com>
Signed-off-by: Aviv Heller <avivh@mellanox.com>
Signed-off-by: Yossi Kuperman <yossiku@mellanox.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>