net: mgmt: Increment API major version number

As per API overview documentation, a braking API change must
increment major version number.

https://docs.zephyrproject.org/latest/develop/api/overview.html#api-overview

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

include/zephyr/net/net_mgmt.h

@@ -24,7 +24,7 @@ extern "C" {
  * @brief Network Management
  * @defgroup net_mgmt Network Management
  * @since 1.7
- * @version 1.0.0
+ * @version 2.0.0
  * @ingroup networking
  * @{
  */