cadence_gem: factor out can_rx() logic replication

The gem_receive() function replicates the logic for whether or not the device
can rx. Just call the actual gem_can_receive() function in place.
Signed-off-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: bf7f93969f3e01fbc76d68d2955307fdbad11bb1.1360901435.git.peter.crosthwaite@xilinx.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/cadence_gem.c

@@ -615,7 +615,7 @@ static ssize_t gem_receive(NetClientState *nc, const uint8_t *buf, size_t size)
     s = qemu_get_nic_opaque(nc);
 
     /* Do nothing if receive is not enabled. */
-    if (!(s->regs[GEM_NWCTRL] & GEM_NWCTRL_RXENA)) {
+    if (!gem_can_receive(nc)) {
         return -1;
     }