Document apps in doxygen module style, create more top-level categories to structure documentation

src/include/lwip/apps/netbiosns.h

@@ -34,13 +34,10 @@
 
 #include "lwip/apps/netbiosns_opts.h"
 
-/** Init netbios responder */
 void netbiosns_init(void);
 #ifndef NETBIOS_LWIP_NAME
-/** Set netbios name. ATTENTION: the hostname must be <= 15 characters! */
 void netbiosns_set_name(const char* hostname);
 #endif
-/** Stop netbios responder */
 void netbiosns_stop(void);
 
 #endif /* LWIP_HDR_APPS_NETBIOS_H */

src/include/lwip/apps/snmp.h

@@ -69,7 +69,10 @@ struct snmp_varbind
   void *value;
 };
 
-/** Agent setup, start listening to port 161. */
+/**
+ * @ingroup snmp_core
+ * Agent setup, start listening to port 161.
+ */
 void snmp_init(void);
 void snmp_set_mibs(const struct snmp_mib **mibs, u8_t num_mibs);