btrfs-progs: qgroup: make --rescan the default behavior after assign

Even though we have --rescan option, it still needs the user to manually
specify it or call quota rescan command.

This does not make much sense for the most common usecase and only
confuses users.  When the rescan is not desired, the --no-rescan option
can be used, eg.  when a mass qgruop assignment happens and the repeated
rescan would slow things down. This is considered a marginal usecase.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/btrfs-qgroup.asciidoc

@@ -47,8 +47,8 @@ identified by <path>.
 `Options`
 +
 --rescan::::
-Automatically schedule quota rescan if the new qgroup assignment leads to
-quota inconsistency.
+(default since: 4.19) Automatically schedule quota rescan if the new qgroup
+assignment would lead to quota inconsistency.
 --no-rescan::::
 Explicitly ask not to do a rescan.
 

cmds-qgroup.c

@@ -40,7 +40,7 @@ static int _cmd_qgroup_assign(int assign, int argc, char **argv,
 {
 	int ret = 0;
 	int fd;
-	bool rescan = false;
+	bool rescan = true;
 	char *path;
 	struct btrfs_ioctl_qgroup_assign_args args;
 	DIR *dirstream = NULL;