Some operations like interface creation may need to return metadata
- in this case, interface name - back to the caller if the operation
is successful.
This change implements attaching an `NLMSGERR_ATTR_COOKIE` nla to the
operation reply message via `nlmsg_report_cookie()`.
Additionally, on successful interface creation, interface index and
interface name are returned in the `IFLA_NEW_IFINDEX` and `IFLA_IFNAME
TLVs, encapsulated in the `NLMSGERR_ATTR_COOKIE`.
Reviewed By: pauamma
Differential Revision: https://reviews.freebsd.org/D38283
MFC after: 1 week
* Separate interface creation from interface modification code
* Support setting some interface attributes (ifdescr, mtu, up/down, promisc)
* Improve interaction with the cloners requiring to parse/write custom
interface attributes
* Add bitmask-based way of checking if the attribute is present in the
message
* Don't use multipart RTM_GETLINK replies when searching for the
specific interface names
* Use ENODEV instead of ENOENT in case of failed RTM_GETLINK search
* Add python netlink test helpers
* Add some netlink interface tests
Differential Revision: https://reviews.freebsd.org/D37668
