ip_tunnel: Move stats allocation to core

ip_tunnel: Move stats allocation to core

With commit 34d21de99cea9 ("net: Move {l,t,d}stats allocation to core and
convert veth & vrf"), stats allocation could be done on net core instead
of this driver.

With this new approach, the driver doesn't have to bother with error
handling (allocation failure checking, making sure free happens in the
right spot, etc). This is core responsibility now.

Move ip_tunnel driver to leverage the core allocation.

All the ip_tunnel_init() users call ip_tunnel_init() as part of their
.ndo_init callback. The .ndo_init callback is called before the stats
allocation in netdev_register(), thus, the allocation will happen before
the netdev is visible.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240607084420.3932875-1-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>