DISPATCH-1274: Separate qd_timer_t lock from server

qd_timer_t was sharing a lock with qd_server_t for historical reasons.
Code inspection shows there is no need for the sharing.

- timer.c calls qd_server_timeout() which is thread-safe, and no other server functions.
- timer calls handlers outside the lock so it doesn't mater what lock is used.
3 files changed