Tools: hv: Gather ipv[4,6] gateway information

Gather information on the default gateways - ipv4/ipv6.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>