- ALPN may not be available:
  - because OpenSSL does not support it.
  - because one of the peers does not support it.
- Tested manually end to end by forcing TSI_OPENSSL_ALPN_SUPPORT to 0.
  Also tested if only one of the peers supports ALPN.

Fixes two warnings in log_win32.c under msvc2015
log_win32.c(109): warning C4013: 'gpr_strdup' undefined; assuming extern returning int
log_win32.c(109): warning C4047: 'return': 'char *' differs in levels of indirection from 'int'

and corrects a typo in an error message

This effectively doubles our qps/core on qps_test on my machine.