libsepol: Use spaceship comparison operator when comparing ibpkeys

The comparsion function for ibpkeys in kernel_to_common subtracts
the subnet_prefixes of the two ibpkeys which are unsigned 64-bit
values and stores the result in an int which might not be able
to contain the result.

Use the spaceship comparison operator to compare the subnet_prefxes
to avoid any issues.

Signed-off-by: James Carter <jwcart2@gmail.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>

Author: jwcart2

libsepol/src/kernel_to_common.c

@@ -585,7 +585,8 @@ static int ibpkey_data_cmp(const void *a, const void *b)
 	struct ocontext *const *aa = a;
 	struct ocontext *const *bb = b;
 
-	rc = (*aa)->u.ibpkey.subnet_prefix - (*bb)->u.ibpkey.subnet_prefix;
+	rc = spaceship_cmp((*aa)->u.ibpkey.subnet_prefix,
+			   (*bb)->u.ibpkey.subnet_prefix);
 	if (rc)
 		return rc;