Decode more flow record types

[Preetam]

Missing:

• TypeEthernetFrameFlow = 2
• TypeIpv6Flow = 4
• TypeExtendedRouterFlow = 1002
• TypeExtendedGatewayFlow = 1003
• TypeExtendedUserFlow = 1004
• TypeExtendedUrlFlow = 1005
• TypeExtendedMlpsFlow = 1006
• TypeExtendedNatFlow = 1007
• TypeExtendedMlpsTunnelFlow = 1008
• TypeExtendedMlpsVcFlow = 1009
• TypeExtendedMlpsFecFlow = 1010
• TypeExtendedMlpsLvpFecFlow = 1011
• TypeExtendedVlanFlow = 1012

[Preetam]

I think this loop needs to keep some sort of state to know if we're dealing with an IPv4 or IPv6 address. The spec shows it as a union:

/* Address types */

typedef opaque ip_v4[4];
typedef opaque ip_v6[16];

enum address_type {
   UNKNOWN  = 0,
   IP_V4    = 1,
   IP_V6    = 2
}

union address (address_type type) {
   case UNKNOWN:
     void;
   case IP_V4:
     ip_v4;
   case IP_V6:
     ip_v6;
}

In that case, I think maybe we can just treat it as a [16]byte and decode it. Is it possible to just look at a [16]byte and tell if it's a v4 or v6 address?

[Preetam]

Note that in this documentation, referring to an IP address
as an IPv4 address or an IPv6 address is a semantic property
of the address, not just the length of the byte slice: a 16-byte
slice can still be an IPv4 address.
— http://golang.org/pkg/net/#IP

Good enough for me.