Reflect the recent change of location for the git repositories, and the
creation of the -next development repo, in README and README.devel.

Also remove the link to the Linux Foundation wiki that contained
information about iproute2. The link is now broken, I did not find any
alternative page to point to.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: David Ahern <dsahern@gmail.com>