Updated Marshal and unmarshal methods to make compatible with protobuf

[vlasfama]

Reffer to #2705

• updated the comment for marshal and unmarshal methods which was created to make protobuf
  compatible.
• Added the marshal,unmarshal,size and MarshalTo methods for nodeinfo.go

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (develop@99b9c9b). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff             @@
##             develop    #2918   +/-   ##
==========================================
  Coverage           ?   62.77%           
==========================================
  Files              ?      212           
  Lines              ?    17409           
  Branches           ?        0           
==========================================
  Hits               ?    10928           
  Misses             ?     5567           
  Partials           ?      914

Impacted Files	Coverage Δ
p2p/node_info.go	75.64% <0%> (ø)