app/testpmd: add TOS and TTL fields to VXLAN encapsulation

app/testpmd: add TOS and TTL fields to VXLAN encapsulation

The new testpmd set vxlan-tos-ttl command is added. It
allows to specify tos and tll fields for encapsulation IP
header.

IPv4 VXLAN outer header:

  testpmd> set vxlan-tos-ttl ip-version ipv4 vni 4 udp-src 4
           udp-dst 4 ip-tos 0 ip-ttl 255 ip-src 127.0.0.1
           ip-dst 128.0.0.1 eth-src 11:11:11:11:11:11
           eth-dst 22:22:22:22:22:22

IPv6 VXLAN outer header:
  testpmd> set vxlan-tos-ttl ip-version ipv6 vni 4 udp-src 4
           udp-dst 4 ip-tos 0 ip-ttl 255 ::1 ip-dst ::2222
           eth-src 11:11:11:11:11:11 eth-dst
           22:22:22:22:22:22

Note: ip-ttl parameter corresponds the nop_limits field for IPv6.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Ori Kam <orika@mellanox.com>