The existing IE.from_dict() method *supposedly* accepts a dict as
input value, but it actually expects the raw decoded value, unless it is
a nested IE. This is inconsistent in various ways, and results in a bug
visible at a higher layer, such as files like EF.{DOMAIN,IMPI,IMPU},
which are transparent files containing a single BER-TLV IE.
Decoding such files worked, but re-encoding them did not, due to the
fact that we'd pass a dict to the from_dict method, which then gets
assigned to self.decoded and further passed along to any later actual
encoder function like to_bytes or to_tlv. In that instance, the dict
might be handed to a self._construct which has no idea how to process
the dict, as it expects the raw decoded value.
Change-Id: I3dd5204510e5c32ef1c4a999258d87cb3f1df8c8
Closes: OS#6073
Related: OS#6072
579ac3ec0e