brei: use memcpy for the 64bit protocol copy

On some architectures (ARM, afaik) addresses needs to be a multiple
of their word size. Since the protocol doesn't enforce alignment on
multiples of 8, let's use a memcpy to copy any 64-bit number instad of
the pointer access.

src/brei-shared.c

@@ -215,7 +215,7 @@ brei_demarshal(struct brei_context *brei, struct iobuf *buf, const char *signatu
 		case 'o':
 		case 'n':
 		case 't':
-			arg->x = *(uint64_t *) p;
+			memcpy(&arg->x, p, sizeof(arg->x));
 			p++;
 			p++;
 			break;