cls_flower: remove mpls_opts_policy

Compiling with W=1 gives the following warning:
net/sched/cls_flower.c:731:1: warning: ‘mpls_opts_policy’ defined but not used [-Wunused-const-variable=]

The TCA_FLOWER_KEY_MPLS_OPTS contains a list of
TCA_FLOWER_KEY_MPLS_OPTS_LSE. Therefore, the attributes all have the
same type and we can't parse the list with nla_parse*() and have the
attributes validated automatically using an nla_policy.

fl_set_key_mpls_opts() properly verifies that all attributes in the
list are TCA_FLOWER_KEY_MPLS_OPTS_LSE. Then fl_set_key_mpls_lse()
uses nla_parse_nested() on all these attributes, thus verifying that
they have the NLA_F_NESTED flag. So we can safely drop the
mpls_opts_policy.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>