Refactor the offload permission check and add tests

- Rename the conntrack destination port check function
- Use CollectionUtils.contains to check the denied ports
- Add tests for the streams with ftp and pptp tcp port are
  not able to be offloaded

Bug: 195914327
Test: atest TetheringCoverageTests
Change-Id: I7e2591bea1f6db46271efb0c30970fb8d4efe1e4
2 files changed