net: sched: Fix dump of MPLS_OPT_LSE_LABEL attribute in cls_flower

TCA_FLOWER_KEY_MPLS_OPT_LSE_LABEL is a u32 attribute (MPLS label is
20 bits long).

Fixes the following bug:

 $ tc filter add dev ethX ingress protocol mpls_uc \
     flower mpls lse depth 2 label 256             \
     action drop

 $ tc filter show dev ethX ingress
   filter protocol mpls_uc pref 49152 flower chain 0
   filter protocol mpls_uc pref 49152 flower chain 0 handle 0x1
     eth_type 8847
     mpls
       lse depth 2 label 0  <-- invalid label 0, should be 256
   ...

Fixes: 61aec25a ("cls_flower: Support filtering on multiple MPLS Label Stack Entries")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>