MD-type 2 support

[upa]

add support MD-Type2 variable length contexts, and remove Network|Service Platform|Shared Contexts.
They have been removed from ietf-sfc-nsh-01? https://tools.ietf.org/html/draft-ietf-sfc-nsh-01

I would be happy if you could merge this commit into the pr the-tcpdump-group#490 .

MD-type 1 and type 2 (no metadata) outputs are shown below.

% sudo ./tcpdump -vvvni eth0 port 4790
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
18:25:58.510999 IP (tos 0x0, ttl 64, id 2016, offset 0, flags [none], proto UDP (17), length 102)
    10.0.2.15.4790 > 10.10.10.10.4790: [no cksum] VXLAN-GPE, flags [IP], vni 10
    NSH, ver 0, flags [], length 6, MD Type 0x1, Next Protocol 0x3, Service Path ID 0x00000b, Service Index 0x5
        Context[00]: 0x00000000
        Context[01]: 0x00000000
        Context[02]: 0x00000000
        Context[03]: 0x00000000
    ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 172.16.0.2 tell 172.16.0.1, length 28

and

% sudo ./tcpdump -vvvni eth0 port 4790
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
18:26:37.302777 IP (tos 0x0, ttl 64, id 7460, offset 0, flags [none], proto UDP (17), length 86)
    10.0.2.15.4790 > 10.10.10.10.4790: [no cksum] VXLAN-GPE, flags [IP], vni 11
    NSH, ver 0, flags [], length 2, MD Type 0x2, Next Protocol 0x3, Service Path ID 0x00000c, Service Index 0x5
    ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 172.16.0.2 tell 172.16.0.1, length 28

[bugyo]

Thank you for your help.
The names of contexts are removed from the draft is certainly true.
I will merge this pull request immediately.

And, I think I have to correct the condition " if(len < 24) " to " if(len < 8) ". Is it reasonable?

[upa]

And, I think I have to correct the condition " if(len < 24) " to " if(len < 8) ". Is it reasonable?

Yes! I missed this point. thank you.
Minimum length is nsh base header + nsh path header = 8 byte (MD-type 2 and no metadata).

[upa]

So sorry,,,

when vflag is not set, contexts are not counted... I fixed this bug.
could you merge this commit upa@d973379 ?

[bugyo]

OK, I merged the commit and packed these commits. Thank you.