[network] Use BTreeMap in handshake msg
[network] Use BTreeMap in handshake msg

Since we want to find the highest common protocol version supported by 2
connected nodes, it's better to use BTreeMap which allows us to iterate
in sorted order.

Closes: #3358
Approved by: phlip9

aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,libra/libra,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core