selftests: net: use upstream mtools

selftests: net: use upstream mtools

Joachim kindly merged the IPv6 support in
https://github.com/troglobit/mtools/pull/2, so we can just use his
version now. A few more fixes subsequently came in for IPv6, so even
better.

Check that the deployed mtools version is 3.0 or above. Note that the
version check breaks compatibility with my fork where I didn't bump the
version, but I assume that won't be a problem.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20240510112856.1262901-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>