Fix build on mingw

Last commit unconditionally included a linux-specific header.

Do not do that.

src/util/virnetdev.c

@@ -47,6 +47,10 @@
 # undef HAVE_STRUCT_IFREQ
 #endif
 
+#if defined(SIOCETHTOOL) && defined(HAVE_STRUCT_IFREQ)
+# include <linux/ethtool.h>
+#endif
+
 #if HAVE_DECL_LINK_ADDR
 # include <sys/sockio.h>
 # include <net/if_dl.h>

src/util/virnetdev.h

@@ -32,7 +32,6 @@
 # include "virpci.h"
 # include "device_conf.h"
 
-# include <linux/ethtool.h>
 # ifdef HAVE_STRUCT_IFREQ
 typedef struct ifreq virIfreq;
 # else