ip: rewrite routel in python

ip: rewrite routel in python

Not sure if anyone uses the routel script. The script was
a combination of ip route, shell and awk doing command scraping.
It is now possible to do this much better using the JSON
output formats and python.

Rewriting also fixes the bug where the old script could not parse
the current output format.  At the end was getting:
/usr/bin/routel: 48: shift: can't shift that many

The new script also has IPv6 as option.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David Ahern <dsahern@kernel.org>