Linux 5.16: Resolve ZSTD_isError symbol collision in Linux kernel

Linux 5.16: Resolve ZSTD_isError symbol collision in Linux kernel

Newer zstd code introduced in the main kernel tree now creates a symbol
collision with ZSTD_isError in our ZSTD code. This change relabels our
implementation with a ZFS-specific symbol name, and undoes some
macro-based micro-optimizations that conflict with the attempt to rename
our internal-use version.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #12819