common: Drop net.h from common header

Move this header out of the common header. Network support is used in
quite a few places but it still does not warrant blanket inclusion.

Note that this net.h header itself has quite a lot in it. It could be
split into the driver-mode support, functions, structures, checksumming,
etc.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/include/asm/eth.h b/arch/sandbox/include/asm/eth.h
index 477fa00..b313bf5 100644
--- a/arch/sandbox/include/asm/eth.h
+++ b/arch/sandbox/include/asm/eth.h
@@ -9,6 +9,8 @@
 #ifndef __ETH_H
 #define __ETH_H
 
+#include <net.h>
+
 void sandbox_eth_disable_response(int index, bool disable);
 
 void sandbox_eth_skip_timeout(void);