hashfn: fix inconsistencies on big-endian architectures (#3979)

The computation of the SuperFashHash function did assume that the code
was run on a little-endian machine, causing a different result when it's
run on a big-endian machine.

This patch explicitly accesses the memory using little-endian mode to
keep backwards compatibility but to produce the same result on
big-endian architectures.

Fixes: #3345

Signed-off-by: Xavi Hernandez <xhernandez@gmail.com>

libglusterfs/src/hashfn.c

@@ -17,7 +17,7 @@
 #include <endian.h>
 #endif
 
-#define get16bits(d) (*((const uint16_t *)(d)))
+#define get16bits(d) le16toh(*((const uint16_t *)(d)))
 
 #define DM_DELTA 0x9E3779B9
 #define DM_FULLROUNDS 10 /* 32 is overkill, 16 is strong crypto */