net: use skb_to_full_sk() in skb_update_prio()

net: use skb_to_full_sk() in skb_update_prio()

Andrei Vagin reported a KASAN: slab-out-of-bounds error in
skb_update_prio()

Since SYNACK might be attached to a request socket, we need to
get back to the listener socket.
Since this listener is manipulated without locks, add const
qualifiers to sock_cgroup_prioidx() so that the const can also
be used in skb_update_prio()

Also add the const qualifier to sock_cgroup_classid() for consistency.

Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
Signed-off-by: Eric Dumazet <[email protected]>
Reported-by: Andrei Vagin <[email protected]>
Signed-off-by: David S. Miller <[email protected]>