Use native netlink code instead of /sbin/ip to manipulate routes

Use native netlink code instead of /sbin/ip to manipulate routes

Shelling out to /sbin/ip is slow, and more importantly it does
not preserve the error messages returned by the kernel when
adding or deleting a route fails.  Instead, use netlink directly.

This change does not yet pass the errors back to CommandListener;
that is done in the next change in the series.

Change-Id: I5ad3c8583580857be6386a620ff5c4f3872d685b