cat: all splice call tries to fallback while GNU do that for 1~2nd call only

[oech3]

$ echo|strace -o /dev/null -e inject=splice:error=ENOSYS:when=3 cat
$ echo|strace -o /dev/null -e inject=splice:error=ENOSYS:when=2 gnu9.11/cat
$ echo|strace -o /dev/null -e inject=splice:error=ENOSYS:when=3 gnu9.11/cat
cat: -: Function not implemented

This does not apply for file input (why?). Related tests/cat/splice.sh.

[oech3]

The behaviour still masks errors not compatible with normal read/write for actual usage.

[oech3]

Plan?

• add uucore::pipes::check_splice_support_using_splice()
• Replace PipeRes with std::io::Error
• do uucore::pipe::check_splice_support_using_splice() at 1st and use normal function