Originally division around sizeof(uint32_t) caused silent truncation
for struct kr_qflags with sizes not multiple of 4 bytes.

Attempts to optimize using uint32_t blocks could lead to read/write
beyond end of uint32_t so I'm not willing to risk it.

Also, the code was refactored to avoid duplication between _set and _clear.
Quick look into assembly produced by gcc 7.2.1 with -O2 on x86_64 confirms that
all auxiliary functions got inlined so there are not extra function calls.

Unit tests are attached. These fail on the previous version of _set() and
_clear() and work now.