Consolidate CMD/EVENT constants into IpClientCommands inner class

* Moved all constants prefixed with CMD_ and EVENT_ from the IpClient
  class into the IpClientCommands inner class.
* This prevents unnecessary execution of MessageUtils.findMessageNames()
  on the entire IpClient class, avoiding potential
  ClassNotFoundException issues when using R+ APIs.

Test: TH
Change-Id: I6486dc60443ee6899c156e7930a1156c82bdddf3
2 files changed