Move check_file to os/$platform section

Keep check_file_generic() in shared code base, and allow special case
code in check_file() in os section. In future, macOS will have
additional checks in check_file().

Linux and FreeBSD wrappers just calls check_file_generic().

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Jorgen Lundman <lundman@lundman.net>
Closes #12385

cmd/zpool/os/linux/zpool_vdev_os.c

@@ -410,3 +410,9 @@ void
 after_zpool_upgrade(zpool_handle_t *zhp)
 {
 }
+
+int
+check_file(const char *file, boolean_t force, boolean_t isspare)
+{
+	return (check_file_generic(file, force, isspare));
+}