Merge branch 'unify_external' into iproute2-next

Serhey Popovych  says:

====================

With this series I want to unify collect metadata
handling in tunnels:

  1) Use "external" name for JSON and non-JSON output.

     Do not *print* any options when tunnel in
     collect metadata mode: gre6 already do
     this, so just apply to others.

  2) Do not *add* any attributes when configuring
     gre tunnel in collect metadata mode.

     Other tunnels (e.g. gre6, iptnl, ip6tnl)
     alredy do that.

This is next step in ipv4 and ipv6 modules
unification to prepare for merge in the future.

Any comments, suggestions and criticism as always
welcome.

v2
  For all tunnels implementing collect metadata
  use "external" keyword for both JSON. Thanks
  to Jiri Benc for detailed explanation.
====================

Signed-off-by: David Ahern <dsahern@gmail.com>