macvtap: convert send / recv function to use libnl

macvtap: convert send / recv function to use libnl

In a second step I am converting the netlink send/receive functions to
use libnl.

I tested this with 802.1Qbg profiles and my test server and did not see
a regression.

Caveat: The online documentation of libnl talks about nl_socket_alloc()
but the header file provides nl_handle_alloc() -- this could be a hint
to a possible problem between libnl versions...

http://www.infradead.org/~tgr/libnl/doc/group__socket.html

versus

http://libnl.sourcearchive.com/documentation/1.1/group__socket_gf903c9ea089735b1ba8e40dae801c47d.html