uwsgi_lock_fast_init fails on Linux 3.14 on BeagleBone Black

Linux 3.14 on the BeagleBone Black doesn't support robust shared mutex, syscall set_robust_list fails with ENOSYS.  When uwsgi_lock_fast_init retries with a standard shared mutex it sets the protocol to PTHREAD_PRIO_INHERIT, which makes pthread_mutex_init fail again.

The change just makes it so the protocol isn't set again.  It still complains about not having robust a mutex, but succeeds making a standard mutex.