Fix changing tunnel remote and local address to any

Fix changing tunnel remote and local address to any

If a tunnel is created with a local address, you can't change it to any.

 # ip tunnel add tunl1 mode ipip remote 10.16.42.37 local 10.16.42.214 ttl 64
 # ip tunnel show tunl1
 tunl1: ip/ip  remote 10.16.42.37  local 10.16.42.214  ttl 64
 # ip tunnel change tunl1 local any
 # echo $?
 0
 # ip tunnel show tunl1
 tunl1: ip/ip  remote 10.16.42.37  local 10.16.42.214  ttl 64

It happens that parse_args zeroes ip_tunnel_parm, and when creating the
tunnel, it is OK to leave it as is if the address is any. However, when
changing the tunnel, the current parameters will be read from
ip_tunnel_parm, and local and remote address won't be zeroes anymore, so
it needs to be explicitly set to any.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>