ipv6: remove extra dev_hold() for fallback tunnels

ipv6: remove extra dev_hold() for fallback tunnels

My previous commits added a dev_hold() in tunnels ndo_init(),
but forgot to remove it from special functions setting up fallback tunnels.

Fallback tunnels do call their respective ndo_init()

This leads to various reports like :

unregister_netdevice: waiting for ip6gre0 to become free. Usage count = 2

Fixes: 293e58f9ff0e ("ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods")
Fixes: 2b0f247a9603 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
Fixes: 5e83eb1b62aa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
Fixes: 6b18d273ffdf ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>