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/board/AndesTech/adp-ag101p/adp-ag101p.c b/board/AndesTech/adp-ag101p/adp-ag101p.c
index d349b19..23cdf4f 100644
--- a/board/AndesTech/adp-ag101p/adp-ag101p.c
+++ b/board/AndesTech/adp-ag101p/adp-ag101p.c
@@ -8,6 +8,7 @@
 #include <common.h>
 #include <flash.h>
 #include <init.h>
+#include <net.h>
 #if defined(CONFIG_FTMAC100) && !defined(CONFIG_DM_ETH)
 #include <netdev.h>
 #endif