fix: win32 tcp_keepalive gets set even when option is -1

The default -1 option value of ZMQ_TCP_KEEPALIVE means to not do anything. However the win32 codepath was not respecting this.

ZMQ_TCP_KEEPALIVE_IDLE and ZMQ_TCP_KEEPALIVE_INTVL options should also behave this way. However it doesn't seem possible to set them separately on Windows platform.

Also fix tabs to spaces.