v2.0.x Chore - improve makefile comments to align with CEP-8

[reactive-firewall]

Consider these improvements for clarity:

in Makefile

-	$(QUIET)test -d "$@" || DO_FAIL="exit 77" ;  # set fail if can't verify directory
-	$(QUIET)test -e "$@" || DO_FAIL="exit 69" ;  # overwrite exitcode if does not exsist.
+	$(QUIET)test -d "$@" || DO_FAIL="exit 77" ;  # Exit 77: Permission denied - can't verify directory
+	$(QUIET)test -e "$@" || DO_FAIL="exit 69" ;  # Exit 69: Service unavailable - directory does not exist