ip link: Add ipvlan support to the iproute2/ip util

ip link: Add ipvlan support to the iproute2/ip util

Adding basic support to create virtual devices using 'ip'
utility. Following is the syntax -

	ip link add link <master> <virtual> type ipvlan mode [ l2 | l3 ]
	e.g. ip link add link eth0 ipvl0 type ipvlan mode l3

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Laurent Chavey <chavey@google.com>
Cc: Tim Hockin <thockin@google.com>
Cc: Brandon Philips <brandon.philips@coreos.com>
Cc: Pavel Emelianov <xemul@parallels.com>