Convert most P2P msg serialization to a new macro with TLV suffixes

Convert most P2P msg serialization to a new macro with TLV suffixes

The network serialization format for all messages was changed some
time ago to include a TLV suffix for all messages, however we never
bothered to implement it as there isn't a lot of use validating a
TLV stream with nothing to do with it. However, messages are
increasingly utilizing the TLV suffix feature, and there are some
compatibility concerns with messages written as a part of other
structs having their format changed (see previous commit).

Thus, here we go ahead and convert most message serialization to a
new macro which includes a TLV suffix after a series of fields,
simplifying several serialization implementations in the process.