BUG/MINOR: thread: use the correct thread's group in ha_tkillall()

In ha_tkillall(), the current thread's group was used to check for the
thread being running instead of using the target thread's group mask.
Most of the time it would not have any effect unless some groups are
uneven where it can lead to incomplete thread dumps for example.

No backport is needed, this is purely 2.7.
1 file changed