Feature/what is network number handling (#304)

* Add What-Is-Network-Number handling.

Add What-Is-Network-Number and Network-Number-Is network layer handling.
Refactor npdu_encode_npdu_network() from router specific code.
Add unit test for NDPU network message
Add app for What-Is-Network-Number
Add app for Network-Number-Is
Add send helper for What-Is-Network-Number
Add send helper for Network-Number-Is

* added sys/debug.c to ports builds for use of debug_printf() in npdu handler.

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

apps/Makefile

@@ -139,7 +139,7 @@ SUBDIRS = lib readprop writeprop readfile writefile reinit server dcc \
 	server-client
 
 ifeq (${BACDL_DEFINE},-DBACDL_BIP=1)
-	SUBDIRS += whoisrouter iamrouter initrouter
+	SUBDIRS += whoisrouter iamrouter initrouter whatisnetnum netnumis
 	ifneq (${BBMD},none)
 	SUBDIRS += readbdt readfdt writebdt
 	endif
@@ -213,6 +213,14 @@ iamrouter: $(BACNET_LIB_TARGET)
 initrouter: $(BACNET_LIB_TARGET)
 	$(MAKE) -b -C $@
 
+.PHONY: whatisnetnum
+whatisnetnum: $(BACNET_LIB_TARGET)
+	$(MAKE) -b -C $@
+
+.PHONY: netnumis
+netnumis: $(BACNET_LIB_TARGET)
+	$(MAKE) -b -C $@
+
 .PHONY: mstpcap
 mstpcap:
 	$(MAKE) -b -C $@