rocker: mark neigh update event processing as 'no wait'

Neigh update event handler runs in a context where we can't sleep, so mark
processing in driver with ROCKER_OP_FLAG_NOWAIT.  NOWAIT will use
GFP_ATOMIC for allocations and will queue cmds to the device's cmd ring but
will not wait (sleep) for cmd response back from device.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>