TLSServer/Client need to include <errno.h> on NetBSD

Same fix applied as per Solaris. See TD-55 and
c60ec0b6ee

ChangeLog

@@ -4,7 +4,7 @@
         to Michele Vetturi).
 - TD-45 Fix preprocessor define (thanks to Jochen Sprickerhof).
 - TD-55 TLSServer/Client need to include <errno.h> on Solaris (thanks to Tatjana
-        Heuser).
+        Heuser). Also applied to NetBSD.
 - TD-56 File.cpp needs to include <string.h> on Solaris (thanks to Tatjana
         Heuѕer).
 - TD-57 taskdctl script assumes /bin/sh is /bin/bash (thanks to Tatjana Heuser).