add bip_get_interface and Device_Time_Of_Restart, fix Network_Port_Changes_Discard (#1038)

* added bip_get_interface

* basic/object/device get/set time of restart

* clear changes pending

* clang-format

src/bacnet/datalink/bip.h

@@ -35,6 +35,9 @@ bool bip_init(char *ifname);
 BACNET_STACK_EXPORT
 void bip_set_interface(const char *ifname);
 
+BACNET_STACK_EXPORT
+const char *bip_get_interface(void);
+
 BACNET_STACK_EXPORT
 void bip_cleanup(void);