r8169: use netif_start_queue instead of netif_wake_qeueue in rtl8169_start_xmit

Replace the call to netif_wake_queue in rtl8169_start_xmit with
netif_start_queue as we don't need to actually wake up the queue since
we are still in mid transmit so we just need to reset the bit so it
doesn't prevent the next transmit.
(Description shamelessly copied from a mail sent by Alex.)

Suggested-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>