MINOR: task/thread: factor out a wake-up condition

The wakeup condition in task_wakeup() is redundant as it is already
validated by the CAS. Better move the __task_wakeup() call there, it
also has the merit of being easier to audit this way. This also reduces
the code size by around 1.8 kB :

  $ size haproxy-?
     text    data     bss     dec     hex filename
  2153806  100208 1307676 3561690  3658da haproxy-1
  2152094  100208 1307676 3559978  36522a haproxy-2
1 file changed