Issues #794 and #901

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

• fixes issues introduced in Ability to auto calculate destination mac address when rewriting destination mutlicast IP addresses #563 where multicast MAC addresses where not properly calculated
  • MAC addresses were corrupt when attempting to match to multicast IP addresses as per this article
  • do not update source MAC addresses - only destination source addresss
• with --seed option keep multicast addresses as multicast and unicast/anycast as unicast/anycast after changes

Validation:

• reviewed all packets in PCAP supplied in [Bug] tcprewrite alters MAC addresses when using --seed option #901
• reviewed all packet alterations in sudo make test.

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