routing_table: Use common netlink parser
This reduces the LOC and redundant netlink parsing logic that is
untested.
It also happens to fix an issue with the current parsing breaking with
some of the routes returned by the kernel
```
[19259.086333] phosphor-network-manager[400]: Refreshing the objects.
[19259.094507] phosphor-network-manager[400]: Error validating header
[19259.095419] phosphor-network-manager[400]: The operation failed internally.
[19259.124862] phosphor-network-manager[400]: Error validating header
[19259.125593] phosphor-network-manager[400]: The operation failed internally.
[19259.143722] phosphor-network-manager[400]: Error validating header
[19259.144569] phosphor-network-manager[400]: The operation failed internally.
[19259.165901] phosphor-network-manager[400]: Error validating header
[19259.169497] phosphor-network-manager[400]: The operation failed internally.
[19259.204178] phosphor-network-manager[400]: Error validating header
[19259.204838] phosphor-network-manager[400]: The operation failed internally.
[19259.223547] phosphor-network-manager[400]: Error validating header
[19259.224302] phosphor-network-manager[400]: The operation failed internally.
[19259.604162] phosphor-network-manager[400]: Error validating header
[19259.605017] phosphor-network-manager[400]: The operation failed internally.
[19259.623701] phosphor-network-manager[400]: Refreshing complete.
```
Change-Id: I00772361090430ff79a5dd1dcf6cc6077f3f55f1
Signed-off-by: William A. Kennington III <wak@google.com>
2 files changed