Make the thread functions a bit easier to use

Make the thread functions a bit easier to use

- Create separate macros for lock and unlock so that it's easier to identify
  which request is being made.

- Initialize *ponce in the SMB_THREAD_ONCE macro in the non-thread-safe case,
  rather than requiring each init function to determine if it's in the
  non-thread-safe case and manually initialize.

Derrell