net: Change the remaining doxygen comments to javadoc style

Change-Id: I942558ca9e4c140145de6e4a1bcebf8d9d16f3d2
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

include/net/net_core.h

@@ -111,7 +111,7 @@ void net_unregister_driver(struct net_driver *drv);
  */
 int net_set_mac(uint8_t *mac, uint8_t len);
 
-/*!
+/**
  * @brief Send a reply packet to the message originator.
  *
  * @details Application can call this function if it has received

net/ip/net_buf.c

@@ -1,4 +1,4 @@
-/*! @file
+/** @file
  @brief Network buffers
 
  Network data is passed between application and IP stack via

net/ip/net_context.c

@@ -1,4 +1,4 @@
-/*! @file
+/** @file
  @brief Network context API
 
  An API for applications to define a network connection.

net/ip/net_init.c

@@ -1,4 +1,4 @@
-/*! @file
+/** @file
  @brief Network initialization
 
  Initialize the network IP stack. Create two fibers, one for reading data