af_packet: fix tracking issues in packet_do_bind()

It appears that my changes in packet_do_bind() were
slightly wrong.

syzbot found that calling bind() twice would trigger
a false positive.

Remove proto_curr/dev_curr variables and rewrite things
to be less confusing (like not having to use netdev_tracker_alloc(),
and instead use the standard dev_hold_track())

Fixes: f1d9268e ("net: add net device refcount tracker to struct packet_type")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Link: https://lore.kernel.org/r/20220107183953.3886647-1-eric.dumazet@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>