Windows: add missing Winsock2.h
Windows: add missing Winsock2.h

needed for gethostname()

google/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,google/or-tools,google/or-tools,google/or-tools,or-tools/or-tools,google/or-tools