Use memcpy for network to host order function on BE hosts

Harmless change replacing "for" by "memcpy". Note that this change
is inside the block reserved to big endian functions.
diff --git a/lib/sdp.c b/lib/sdp.c
index 3e3a8f8..e782aec 100644
--- a/lib/sdp.c
+++ b/lib/sdp.c
@@ -64,9 +64,7 @@
 #define ntoh64(x) (x)
 static inline void ntoh128(const uint128_t *src, uint128_t *dst)
 {
-	int i;
-	for (i = 0; i < 16; i++)
-		dst->data[i] = src->data[i];
+	memcpy(dst, src, sizeof(uint128_t));
 }
 
 static inline void btoh128(const uint128_t *src, uint128_t *dst)