testsuite: Add mpls packet matching tests for tc flower

testsuite: Add mpls packet matching tests for tc flower

Match all MPLS fields using smallest and highest possible values.
Test the two ways of specifying MPLS header matching:

  * with the basic mpls_{label,tc,bos,ttl} keywords (match only on the
    first LSE),

  * with the more generic "lse" keyword (allows matching at different
    depth of the MPLS label stack).

This test file allows to find problems like the one fixed by
Linux commit 7fdd375e3830 ("net: sched: Fix dump of MPLS_OPT_LSE_LABEL
attribute in cls_flower").

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>