Revert "ip6tunnel: fix 'ip -6 {show|change} dev <name>' cmds"

Revert "ip6tunnel: fix 'ip -6 {show|change} dev <name>' cmds"

This reverts commit ba126dcad20e6d0e472586541d78bdd1ac4f1123.
It breaks tunnel creation when using 'dev' parameter:

$ ip link add type dummy
$ ip -6 tunnel add ip6tnl1 mode ip6ip6 remote 2001:db8:ffff:100::2 local 2001:db8:ffff:100::1 hoplimit 1 tclass 0x0 dev dummy0
add tunnel "ip6tnl0" failed: File exists

dev parameter must be used to specify the device to which
the tunnel is binded, and not the tunnel itself.

Reported-by: Jianwen Ji <jiji@redhat.com>
Reviewed-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: Andrea Claudi <aclaudi@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>