Add bridge interface to documentation

src/include/netif/bridgeif_opts.h

@@ -40,6 +40,12 @@
 
 #include "lwip/opt.h"
 
+/**
+ * @defgroup bridgeif_opts Options
+ * @ingroup bridgeif
+ * @{
+ */
+
 /** BRIDGEIF_PORT_NETIFS_OUTPUT_DIRECT==1: set port netif's 'input' function
  * to call directly into bridgeif code and on top of that, directly call into
  * the selected forwarding port's 'linkoutput' function.
@@ -82,4 +88,8 @@
 #define BRIDGEIF_FW_DEBUG                   LWIP_DBG_OFF
 #endif
 
+/**
+ * @}
+ */
+
 #endif /* LWIP_HDR_NETIF_BRIDGEIF_OPTS_H */