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/cmd/nvedit.c b/cmd/nvedit.c
index 966c134..a86063d 100644
--- a/cmd/nvedit.c
+++ b/cmd/nvedit.c
@@ -29,6 +29,7 @@
 #include <console.h>
 #include <env.h>
 #include <env_internal.h>
+#include <net.h>
 #include <search.h>
 #include <errno.h>
 #include <malloc.h>