net: thunderx: add workqueue control structures for handle ndo_set_rx_mode request

The kernel calls ndo_set_rx_mode() callback from atomic context which
causes messaging timeouts between VF and PF (as they’re implemented via
MSIx). So in order to handle ndo_set_rx_mode() we need to get rid of it.

This commit implements necessary workqueue related structures to let VF
queue kernel request processing in non-atomic context later.

Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>