The function nmbs_strerror does not handle the error code
NMBS_ERROR_INVALID_UNIT_ID inside the switch statement, which triggers
the GCC/Clang Wswitch-enum warning. Adding a new case inside the switch
statement solves this warning.
There is a cast from a const void pointer to an uint8_t pointer inside
the function nmbs_send_raw_pdu, which triggers the GCC/Clang Wcast-qual
warning. Adding the missing const qualifier solves this warning.
Having access to this function is useful in a variety of cases:
- hand-crafting PDUs for unit tests
- implementing extensions of the protocol
- reusing the code for other purposes (e.g. firmware integrity check)
I think this makes the code easier to read, since you can tell whether each
function call will actually `send` some bytes over the wire, or if it will
just `put` some bytes into the buffer.
