Nagasena EXI library encodes xml incorrectly

See https://git.opendaylight.org/gerrit/#/c/5678/13/opendaylight/netconf/netconf-util/src/test/java/org/opendaylight/controller/netconf/util/EXILibTest.java

The encoding process succeeds, but decoding then fails. The problem is namespace handling and appears only when using SAX Transformer to encode DOM to EXI.

There is a workaround in https://git.opendaylight.org/gerrit/#/c/5678/13/opendaylight/netconf/netconf-util/src/main/java/org/opendaylight/controller/netconf/util/handler/NetconfMessageToEXIEncoder.java but it needs to be fixed.

We need to pinpoint the issue and if it really is a nagasena bug, then
we need either to fix nagasena library ourselves and propose a patch:
https://sourceforge.net/projects/openexi/
or report the issue to nagasena developers and wait for them to fix it.