fstests: check for filesystem FS_IOC_FSSETXATTR support

With "_require_xfs_io_command chattr <letter>", check that
flag can be set/cleared using FS_IOC_FSSETXATTR ioctl, similar
to "_require_chattr <letter>" and FS_IOC_SETFLAGS ioctl.

Update the documentation and the tests that use
"_require_xfs_io_command chattr" to test filesystem support
and not only xfs_io support.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/553

@@ -21,7 +21,7 @@ trap "_cleanup; exit \$status" 0 1 2 3 7 15
 workdir="$TEST_DIR/test-$seq"
 _cleanup()
 {
-	$CHATTR_PROG -i $workdir/immutable > /dev/null 2>&1
+	$XFS_IO_PROG -f -r -c "chattr -i" $workdir/immutable >/dev/null 2>&1
 	cd /
 	rm -f $tmp.*
 }
@@ -37,9 +37,8 @@ _supported_fs generic
 rm -f $seqres.full
 
 _require_test
-_require_chattr i
 _require_xfs_io_command "copy_range"
-_require_xfs_io_command "chattr"
+_require_xfs_io_command "chattr" "i"
 
 rm -rf $workdir
 mkdir $workdir