net_sched: cake: use qdisc_pkt_segs()

Use new qdisc_pkt_segs() to avoid a cache line miss in cake_enqueue()
for non GSO packets.

cake_overhead() does not have to recompute it.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251121083256.674562-7-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>