Add native NETMAP driver

Add native NETMAP driver

This is first drop of native NETMAP driver.
It is mainly tested with NETMAP pipes but also
support for native interfaces should work.

New CLI:
create netmap [<intf name>|valeXXX:YYY] [hw-addr <mac>] [pipe]
[master|slave]

Following example creates NETMAP pipe where VPP acts as master:

 create netmap name vale00:vpp1 pipe master

then NETMAP pkt-gen tool can be used to send traffic:

 pkt-gen -i vale00:vpp1}0  -f tx

Change-Id: Ie0ddaa5facc75285b78467420e8a9f9c8dfc39e5
Signed-off-by: Damjan Marion <damarion@cisco.com>