BAddr: add missing define

system/BAddr.h

@@ -48,6 +48,9 @@
 #define BADDR_TYPE_NONE 0
 #define BADDR_TYPE_IPV4 1
 #define BADDR_TYPE_IPV6 2
+#ifndef BADVPN_USE_WINAPI
+    #define BADDR_TYPE_UNIX 3 // only a domain number for BSocket
+#endif
 
 #define BADDR_MAX_ADDR_LEN 128