Fix a few compile errors and warnings found in build testing

drivers/wireless/spirit/drivers/spirit_netdev.c

@@ -1238,7 +1238,7 @@ static void spirit_interrupt_work(FAR void *arg)
       DEBUGVERIFY(spirit_management_rxstrobe(spirit));
       DEBUGVERIFY(spirit_command(spirit, CMD_RX));
 
-      if (priv->state == DRIVER_STATE_SENDING);
+      if (priv->state == DRIVER_STATE_SENDING)
         {
           priv->state = DRIVER_STATE_IDLE;
         }

net/devif/devif_forward.c

@@ -90,6 +90,8 @@ void devif_forward(FAR struct forward_s *fwd)
 
   fwd->f_dev->d_sndlen = 0;
   fwd->f_dev->d_len    = offset;
+
+  UNUSED(ret);
 }
 
 #endif /* CONFIG_NET_IPFORWARD */

net/ipforward/ipfwd_poll.c

@@ -40,11 +40,13 @@
 #include <nuttx/config.h>
 
 #include <stdint.h>
+#include <debug.h>
 
 #include <nuttx/net/netdev.h>
 #include <nuttx/net/net.h>
 
 #include "devif/devif.h"
+#include "sixlowpan/sixlowpan.h"
 #include "ipforward/ipforward.h"
 
 #ifdef CONFIG_NET_IPFORWARD