improve the recommendations on byteswapping calls
improve the recommendations on byteswapping calls

It is very frequent to find userspace code including <asm/byteorder.h>
and/or using/redefining cpu_to_*, *_to_cpu, swabxx from the linux kernel
headers. Add a note asking people to stick to the glibc API.

icke2063/libabcc,LeSpocky/libabc,LeSpocky/libabc,gbenson/libi8x,icke2063/libabcc,gbenson/libi8x