[core] Round packet size to nearest 4 for validation

[sruon]

I affirm:

• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

What I should have done originally instead of adding padding to packets.
Ensures we line up with client 4-byte alignment on all packets.

Steps to test these changes

• GP_CLI_COMMAND_TROPHY_ABSENCE
• GP_CLI_COMMAND_GROUP_LEAVE
• GP_CLI_COMMAND_GROUP_BREAKUP
• GP_CLI_COMMAND_GROUP_LIST_REQ
• GP_CLI_COMMAND_GROUP_CHANGE2
• GP_CLI_COMMAND_CHAT_STD
• GP_CLI_COMMAND_CHAT_NAME
• GP_CLI_COMMAND_ASSIST_CHANNEL
• GP_CLI_COMMAND_GROUP_COMLINK_MAKE