Move system header includes from network.h to network.c

[iphydf]

This change is 

[nurupo]

This looks like something that might be worth testing on all CI configurations once this is ready for merge, as we had quite the trouble with all those OS-specific network includes before.

[iphydf]

Yes, I will do that once 0.2.0 is released.

[iphydf]

@nurupo done.

[iphydf]

https://travis-ci.org/TokTok/c-toxcore/builds/354138261

[sudden6]

Reviewed 33 of 34 files at r1.
Review status: 30 of 34 files reviewed at latest revision, all discussions resolved.

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toxcore/network.c, line 64 at r1 (raw file):

#include <winsock2.h>

#include <windows.h>

add a guard comment like above?

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toxcore/TCP_server.c, line 251 at r1 (raw file):

uint16_t read_TCP_length(Socket sock)
{
    unsigned int count = net_socket_data_recv_buffer(sock);

const

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Comments from Reviewable

[iphydf]

Review status: 25 of 34 files reviewed at latest revision, 2 unresolved discussions.

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toxcore/network.c, line 64 at r1 (raw file):

Previously, sudden6 wrote…

add a guard comment like above?

Done.

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toxcore/TCP_server.c, line 251 at r1 (raw file):

Previously, sudden6 wrote…

const

Done.

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Comments from Reviewable

[sudden6]

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Reviewed 3 of 3 files at r2, 6 of 6 files at r3.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable