Merge branch 'ipv6_tunnel'

Steffen Klassert says:

====================
ipv6: Return an error when adding an already existing tunnel

The ipv6 tunnel locate functions should not return an existing
tunnel if create is true. Otherwise it is possible to add the
same tunnel multiple times without getting an error.

All our ipv6 tunnels have this bug from the very beginning.
Only the sit tunnel was fixed some years ago with:

commit 8db99e57 ("sit: Fail to create tunnel, if it already exists").

This patchset fixes the remaining ipv6 tunnels.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>