legal: add missing hash files and fix date-cpp hash filename

Add missing *.hash files for all board packages using the ix-board macro;
they declare LICENSE_FILES = LICENSE but had no hash file, producing a
warning during make legal-info.

Fix the date-cpp package where the hash file was named date.hash instead
of date-cpp.hash (package name is derived from the directory, not the mk
filename), causing Buildroot to skip the hash check entirely.

Add hash files for local-site packages confd-test-mode, netd, and
onieprom that declared LICENSE_FILES but provided no hash.

Also, rename package/date-cpp/date.mk to date-cpp.mk.  Buildroot derives
the package name from the directory name, so the mk file must match. To
handle the archive name different we set DATE_CPP_SOURCE.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

package/date-cpp/date-cpp.hash

@@ -0,0 +1,3 @@
+# Locally calculated 
+sha256  c90f6c00fb961170560299cbda28ca2d45804913aa8b2a9f36dbb8e0028d6930  LICENSE.txt
+sha256  7a390f200f0ccd207e8cff6757e04817c1a0aec3e327b006b7eb451c57ee3538  date-3.0.1.tar.gz