byteorder: replace __u32

byteorder: replace __u32

In {big,little}_endian.h the changes are entirely mechanical, except for
dealing with casting away of const from pointers-to-const on lines
touched anyway.

In swab.h the casting of constants is done away with as well - I simply
don't see what the respective comment is concerned about in our
environment (sizeof(int) >= 4, sizeof(long) >= {4,8} depending on
architecture, sizeof(long long) >= 8). The comment is certainly relevant
in more general cases. Excess parentheses are dropped as well,
___swab32()'s local variable is renamed, and __arch__swab32()'s is
dropped as being redundant with ___swab32()'s.

The masking operation is also dropped from __fswab64().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Frediano Ziglio <frediano.ziglio@cloud.com>