liburing: support sqe group

Test sqe group feature by combining all related sqe flags.

Also covers group leader/member failure, and such failure in case of
linked groups.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>

Author: ming1

test/Makefile

@@ -225,6 +225,7 @@ test_srcs := \
 	wakeup-hang.c \
 	wq-aff.c \
 	xattr.c \
+	sqe_group.c \
 	# EOL
 
 all_targets :=