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/lib/uuid.c b/lib/uuid.c
index bdb1378..f94c6ab 100644
--- a/lib/uuid.c
+++ b/lib/uuid.c
@@ -5,6 +5,7 @@
 
 #include <common.h>
 #include <env.h>
+#include <rand.h>
 #include <time.h>
 #include <uuid.h>
 #include <linux/ctype.h>