net: ip_tunnel: Don't set tunnel->net in ip_tunnel_init()

ip_tunnel_init() is called from register_netdevice(). In all code paths
reaching here, tunnel->net should already have been set (either in
ip_tunnel_newlink() or __ip_tunnel_create()). So don't set it again.

Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250219125039.18024-6-shaw.leon@gmail.com


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