app/testpmd: fix MPLS BoS bit default value

app/testpmd: fix MPLS BoS bit default value

The Bottom-of-Stack (bos) bit of MPLS indicates
whether its the last MPLS layer (1) or not (0).

Indicating that the encapsulating MPLS is the
last MPLS layer in the packet as the default
behavior is more appropriate since multiple
encapsulation actions is not supported.

Fixes: 3e77031be855 ("app/testpmd: add MPLSoGRE encapsulation")
Fixes: 3e77031be855 ("app/testpmd: add MPLSoGRE encapsulation")
Fixes: a1191d39cb57 ("app/testpmd: add MPLSoUDP encapsulation")
cc: stable@dpdk.org

Signed-off-by: Saleh Alsouqi <salehals@mellanox.com>
Acked-by: Ori Kam <orika@mellanox.com>