This variable ended up being used only on the fast-transition path. On
the re-associate path it was never used, but memcpy-ied nevertheless.
Since its only use is by auth_proto based protocols, move it to the
auth_proto object directly.
Due to how prepare_ft works (we need prev_bssid from the handshake, but
the handshake is reset), have netdev_ft_* methods take an 'orig_bss'
parameter, similar to netdev_reassociate.
This is a new concept applying to any protocol working over authenticate
and/or associate frames (OWE/SAE/FILS). All these protocols behave
similarly enough that they can be unified into a handshake driver
structure.
Now, each protocol will initialize this auth_proto structure inside
their own internal data. The auth_proto will be returned from
the initializer which netdev can then use to manage the protocol by
forwarding authenticate/associate frames into the individual drivers.
The auth_proto consists only of function pointers:
start - starts the protocol
free - frees the driver data
rx_authenticate - receive authenticate frame
rx_associate - receive associate frame
auth_timeout - authenticate frame timed out
assoc_timeout - associate frame timed out
