Combine ethtool-{bitops,util}.h into internal.h

ethtool-util.h contains all kinds of declarations, not just utility
functions or macros.

ethtool-bitops.h contains just a few extra definitions, and its only
user also includes ethtool-util.h.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
diff --git a/pcnet32.c b/pcnet32.c
index 1dac02d..b87cee7 100644
--- a/pcnet32.c
+++ b/pcnet32.c
@@ -2,7 +2,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
-#include "ethtool-util.h"
+#include "internal.h"
 
 #define BIT0  0x0001
 #define BIT1  0x0002