Add back-up implementation of be32toh()

Older systems may not have the be32toh function defined. Check for this
and fall back to checking the endianness and calling bswap_32 directly
if needed.  This works on both old and new systems.

[Thomas De Schampheleire <[email protected]>:
address comments raised by Lucas De Marchi [1], update commit message]
[1] http://www.spinics.net/lists/linux-modules/msg01129.html
diff --git a/libkmod/missing.h b/libkmod/missing.h
index 8d47af8..4c0d136 100644
--- a/libkmod/missing.h
+++ b/libkmod/missing.h
@@ -43,3 +43,13 @@
 		memcpy(__new, __old, __len);				\
 	 })
 #endif
+
+#if !HAVE_DECL_BE32TOH
+#include <endian.h>
+#include <byteswap.h>
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define be32toh(x) bswap_32 (x)
+#else
+#define be32toh(x) (x)
+#endif
+#endif