dyups: fix unlocking behavior

[harry-xm]

Fix #1661

[chobits]

After patching wget https://github.com/alibaba/tengine/pull/1664.patch, cases passed

tests/nginx-tests/tengine-tests/dyups.t .. ok
All tests successful.
Files=1, Tests=78, 10 wallclock secs ( 0.04 usr  0.00 sys +  0.19 cusr  0.27 csys =  0.50 CPU)
Result: PASS

[chobits]

Although the code logic has bug, it will not cause real damage to nginx.
Because ngx_shmtx_unlock() will not unlock other worker's lock, it check the pid number with mutex, if the pid number(mutex lock) is not pid of current worker, it does nothing.