dahdi: Remove call to lock_kernel when calling unlocked_ioctl.

The Big Kernel Lock removal is no longer experimental so we can eliminate the
call to lock_kernel when calling unlock_ioctl.

Internal-Issue-ID: ABE-2904
Signed-off-by: Shaun Ruffell <sruffell@digium.com>
dahdi: Decrease dahdi_timer_lock contention.

On SMP systems there isn't a need for all dahdi timers to
synchronize on dahdi_timer_lock. Instead give each timer it's own
lock to synchronize with process_timers and use dahdi_timer_lock to
protect the global list of locks.

Also, the dahdi_timers list now only contains timers that are set to
fire. This eliminates a test for each timer in the hot path of the
process_masterspan context.

Reduces system load on many-core systems which are heavy users of
DAHDI timers.

Internal-Issue-ID: ABE-2904
Signed-off-by: Shaun Ruffell <sruffell@digium.com>
dahdi: Give timers their own file_operations

Trades the memory of a file_operations structure to eliminate some tests in the
timer operations.

Internal-Issue-ID: ABE-2904
Signed-off-by: Shaun Ruffell <sruffell@digium.com>