api: Disable api_net when DM is used

When CONFIG_API is selected with DM_ETH this
error is present:
api/api_net.c: In function 'dev_enum_net':
api/api_net.c:61:35: warning: initialization from incompatible pointer
type
  struct eth_device *eth_current = eth_get_dev();
                                   ^
api/api_net.c:68:39: error: dereferencing pointer to incomplete type
  memcpy(di->di_net.hwaddr, eth_current->enetaddr, 6);
                                       ^
Disable api_net functions when ETH_DM is selected.
Signed-off-by: NChris Johns <chrisj@rtems.org>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

api/api_net.c

@@ -25,7 +25,7 @@ DECLARE_GLOBAL_DATA_PTR;
 
 #define errf(fmt, args...) do { printf("ERROR @ %s(): ", __func__); printf(fmt, ##args); } while (0)
 
-#ifdef CONFIG_CMD_NET
+#if defined(CONFIG_CMD_NET) && !defined(CONFIG_DM_ETH)
 
 static int dev_valid_net(void *cookie)
 {