Some minor documentation fixes

src/core/netif.c

@@ -1405,6 +1405,7 @@ netif_find(const char *name)
  * @ingroup netif
  * Add extended netif events listener
  * @param callback pointer to listener structure
+ * @param fn callback function
  */
 void netif_add_ext_callback(netif_ext_callback_t* callback, netif_ext_callback_fn fn)
 {

src/include/lwip/netif.h

@@ -505,6 +505,11 @@ struct netif* netif_get_by_index(u8_t idx);
 #define netif_get_index(netif)      ((netif)->num + 1)
 #define NETIF_NO_INDEX              (0)
 
+/**
+ * @ingroup netif
+ * Extended netif callback reasons enumeration.
+ * May be extended in the future!
+ */
 typedef enum
 {
   /** netif was added. num: 0; arg: NULL */

src/include/lwip/opt.h

@@ -2478,8 +2478,8 @@
  */
 
 /**
- * LWIP_HOOK_FILENAME: Custom filename to #include in files that provide hooks.
+ * LWIP_HOOK_FILENAME: Custom filename to \#include in files that provide hooks.
- * Declare your hook function prototypes in there, you may also #include all headers
+ * Declare your hook function prototypes in there, you may also \#include all headers
  * providing data types that are need in this file.
  */
 #ifdef __DOXYGEN__