Add IPv4Address::from_prefix_length

include/tins/ip_address.h

@@ -53,6 +53,13 @@ public:
      */
     static const IPv4Address broadcast;
 
+    /**
+     * \brief Constructs an IPv4 address from a prefix length
+     *
+     * \param prefix_length The length of the prefix
+     */
+    static IPv4Address from_prefix_length(uint32_t prefix_length);
+
     /**
      * \brief Constructor taking a const char*.
      *