rule add creates invalid rule entries

[gthiemonge]

Using pyroute2 0.7.1, adding rules leads to incorrect entries in the rule list, and the rules are not correctly applied by the kernel.

(Issue detected in the OpenStack Octavia project)

I reproduced it with this simple script:

import pyroute2

with pyroute2.IPRoute() as ipr:
    ipr.rule('add', src="10.1.1.1", src_len=32, table=1)

then ip rule shows a strange entry that contains a none field:

$ ip rule | grep 10.1
32000:  from 10.1.1.1 lookup 1 none

Note: 0.6.13 doesn't have this issue