Add utilities to generate packets

This change adds utility methods to generate packets incrementally. It
supports UDP, ESP, IPv4, IPv6 packet generation.

For ESP, it exclusively does AES-CBC, HMAC-SHA256.

Bug: 72950854
Test: This
Change-Id: Icffeed2ebb2005d79faf04f48fd5126d1d6fb175
4 files changed
tree: c8ceac21c34304e6e00556fd8ad5a9820c651bb3
  1. tests/