net: dst.h: Fix shifting signed 32-bit value by 31 bits problem

Fix DST_FEATURE_ECN_CA to use "U" cast to avoid shifting signed
32-bit value by 31 bits problem.
Signed-off-by: Vandana BN <bnvandana@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dst.h

@@ -183,7 +183,7 @@ static inline void dst_metric_set(struct dst_entry *dst, int metric, u32 val)
 }
 
 /* Kernel-internal feature bits that are unallocated in user space. */
-#define DST_FEATURE_ECN_CA	(1 << 31)
+#define DST_FEATURE_ECN_CA	(1U << 31)
 
 #define DST_FEATURE_MASK	(DST_FEATURE_ECN_CA)
 #define DST_FEATURE_ECN_MASK	(DST_FEATURE_ECN_CA | RTAX_FEATURE_ECN)