Add IPv6 support. Add parsing of VLAN and QinQ tagged ethernet packets

[cmoeller-dx]

IPv6:
This commit adds the ability to parse packets, captured by ipv6 speakers.
It is also possible to parse multiprotocol BGP-messages. IPv4 (testing required) and IPv6 are understood protocols.

Filtering source and destination ipv6 addresses is also possible. Filtering REACH_NLRI and UNREACH_NLRI fields are currently not implemented.

Output could look like this:

[BGPMessage UPDATE] - 134 Bytes
|- MAC: 08:ec:f5:2a:8f:c9 -> 40:a6:b7:03:d1:28
|- IP: [1337:7f8:0:0:0:c4:0:1]:23492 -> [de34:7f8:0:0:0:42:ace:666]:179
|- Timestamp: 2020-08-03 18:49:01.458039 (1596480541.458039)
|
|- Path Attributes: 
|--- MP_REACH_NLRI:
|----- Next Hop:
|----- 1337:7f8:0:0:0:c5:0:1
|----- 1337:0:0:0:aec:ace:eac:ce1
|----- 
|----- NLRI:
|----- 1337:42:95::/48
.
.
.

Because of the differnces between ipv4 and ipv6 i changed the signature of the following classmethod

BGPRoute.from_binary(cls, prefix, prefix_length) 
-> 
BGPRoute.from_binary(cls, prefix, prefix_length, proto=BGPStatics.IP4_CODE)

This allows us to interpret ipv6 prefixes. The only thing which is not implemented is the ability to represent the ipv6 address as a number (16byte int). For consistency reason, i understand why one would implement a BGPRoute.decimal_ip_to_string() function for ipv6, but its not necessary at this point since its not used.
Feel free to contribute if you want to :)

VLAN/QinQ:
Ethernet frames containing a VLAN or QinQ tag are now able to be processed.
Filtering is also possible: --filter-service-vlan --filter-customer-vlan
If theres a VLAN tag only, use --filter-customer-vlan

With this commit no options or filter syntax changed, so you can use the parser just like before that commit.