l2tp: take a reference for kernel sockets in l2tp_tunnel_sock_lookup
l2tp: take a reference for kernel sockets in l2tp_tunnel_sock_lookup

When looking up the tunnel socket in struct l2tp_tunnel, hold a reference
whether the socket was created by the kernel or by userspace.

Signed-off-by: Tom Parkin <ea112d67cab4b46373b4d6536b035de78635308d@katalix.com>
Signed-off-by: James Chapman <d87d459960487ecb1b999dfc309f5d5f521df082@katalix.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs