quiche.h: include correct header on Windows
quiche.h: include correct header on Windows

Motivation:

https://github.com/cloudflare/quiche/commit/93c1970b2b1d2c4b0f684210bc7253befec72091 added the sys/socket.h header to quiche.h which does break things on windows.

Modifications:

Only use sys/socket.h if not build on windows, if on windows include winsock2.h

Result:

quiche.h can be used on windows again as well
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