simplify logic to check whether a BSR fits and, if so, which type.
before the check has been done in two places.
we now also accomodate for the CE subheader size.
before the BSR was extracted but the actual index (between 0 and 63)
was not stored but directly converted into bytes.
for log parsing and debugging it is easier to follow the index
value. this patch therefore adds both values to the log message
and extends the API accordingly.
when adding a new subheader to a MAC PDU we should only add the subheader
if at least 2 bytes are left in the PDU. Even a 1 Byte MAC Control Element requires
another byte to pack the subheader.
This fixes#1424 in which a 3 B MAC opportunity is provided in the UL. After
adding the Short BSR, we tried to add another MAC subheader. Adding the subheader
succeeded even though no space is left to add a single byte. With this patch,
adding the subheader fails and the generates MAC PDU is correct.