[master] Fixed db_lost_callback default to NULL build issue

Replaced = NULL with = 0 in dhcpsrv header files altered for 5477.

src/lib/dhcpsrv/cfg_db_access.h

@@ -68,7 +68,7 @@ public:
     /// @param db_lost_callback function to invoke if connectivity to
     /// either the lease or host managers, once established, is subsequently
     /// lost.
-    void createManagers(DatabaseConnection::DbLostCallback db_lost_callback = NULL) const;
+    void createManagers(DatabaseConnection::DbLostCallback db_lost_callback = 0) const;
 
     /// @brief Unparse an access string
     ///

src/lib/dhcpsrv/database_connection.h

@@ -150,7 +150,7 @@ public:
     /// @param db_lost_callback  Optional call back function to invoke if a
     ///        successfully open connection subsequently fails
     DatabaseConnection(const ParameterMap& parameters,
-        DbLostCallback db_lost_callback = NULL)
+        DbLostCallback db_lost_callback = 0)
         :parameters_(parameters), db_lost_callback_(db_lost_callback) {
     }
 

src/lib/dhcpsrv/host_data_source_factory.h

@@ -67,7 +67,7 @@ public:
     /// @throw isc::dhcp::InvalidType The "type" keyword in dbaccess does not
     ///        identify a supported backend.
     static void create(const std::string& dbaccess,
-                       DatabaseConnection::DbLostCallback db_lost_callback = NULL);
+                       DatabaseConnection::DbLostCallback db_lost_callback = 0);
 
     /// @brief Destroy host data source
     ///

src/lib/dhcpsrv/host_mgr.h

@@ -73,7 +73,7 @@ public:
     /// @param db_lost_callback function to invoke if connectivity to
     /// the host database is lost.
     static void create(const std::string& access = "",
-                       DatabaseConnection::DbLostCallback db_lost_callback = NULL);
+                       DatabaseConnection::DbLostCallback db_lost_callback = 0);
 
     /// @brief Returns a sole instance of the @c HostMgr.
     ///

src/lib/dhcpsrv/lease_mgr_factory.h

@@ -71,7 +71,7 @@ public:
     /// @throw isc::dhcp::InvalidType The "type" keyword in dbaccess does not
     ///        identify a supported backend.
     static void create(const std::string& dbaccess, 
-                       DatabaseConnection::DbLostCallback db_lost_callback = NULL);
+                       DatabaseConnection::DbLostCallback db_lost_callback = 0);
 
     /// @brief Destroy lease manager
     ///

src/lib/dhcpsrv/pgsql_host_data_source.h

@@ -61,7 +61,7 @@ public:
     /// @throw isc::dhcp::DbOperationError An operation on the open database has
     ///        failed.
     PgSqlHostDataSource(const DatabaseConnection::ParameterMap& parameters,
-                        DatabaseConnection::DbLostCallback db_lost_callback = NULL); 
+                        DatabaseConnection::DbLostCallback db_lost_callback = 0);
 
     /// @brief Virtual destructor.
     /// Frees database resources and closes the database connection through

src/lib/dhcpsrv/pgsql_lease_mgr.h

@@ -59,7 +59,7 @@ public:
     /// @throw isc::dhcp::DbOperationError An operation on the open database has
     ///        failed.
     PgSqlLeaseMgr(const DatabaseConnection::ParameterMap& parameters,
-                  DatabaseConnection::DbLostCallback db_lost_callback = NULL);
+                  DatabaseConnection::DbLostCallback db_lost_callback = 0);
 
     /// @brief Destructor (closes database)
     virtual ~PgSqlLeaseMgr();