ipip, sit: copy parms.name after register_netdevice

Same fix as 731abb9c for ipip and sit tunnel.
Commit 1c5cae81 removed an explicit call to dev_alloc_name in
ipip_tunnel_locate and ipip6_tunnel_locate, because register_netdevice
will now create a valid name, however the tunnel keeps a copy of the
name in the private parms structure. Fix this by copying the name back
after register_netdevice has successfully returned.

This shows up if you do a simple tunnel add, followed by a tunnel show:

$ sudo ip tunnel add mode ipip remote 10.2.20.211
$ ip tunnel
tunl0: ip/ip  remote any  local any  ttl inherit  nopmtudisc
tunl%d: ip/ip  remote 10.2.20.211  local any  ttl inherit
$ sudo ip tunnel add mode sit remote 10.2.20.212
$ ip tunnel
sit0: ipv6/ip  remote any  local any  ttl 64  nopmtudisc 6rd-prefix 2002::/16
sit%d: ioctl 89f8 failed: No such device
sit%d: ipv6/ip  remote 10.2.20.212  local any  ttl inherit

Cc: stable@vger.kernel.org
Signed-off-by: Ted Feng <artisdom@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>