This commit fixes PUSH FOTA when opaque content-format is used.
This consists of the following fixes:
* Moved `struct block_context` to a private header, so that it can be a
part of `struct lwm2m_input_context`. This allows content decoders to
make use of the block context data.
* Removed faulty `get_length_left` function from the plain text
decoder, and replace it with coap_packet_get_payload() to obtain the
actual payload size.
* Introduce `struct lwm2m_opaque_context` as a part of block context,
which allows to keep track of opaque data download progress.
* Simplify `lwm2m_write_handler_opaque()` function. It will now only
make calls to `engine_get_opaque` - it's the decoder responsibility
to update the opaque context according to it's content format (for
instance TLV decoder should only update it with the actual opaque
data size, not the whole TLV).
Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
12e1fd653d