gen-art-25

[petithug]

• "the generation counters should" -> "the generation counters SHOULD"
• "An implementation could use." -> "An implementation MAY use"
• "the node confirms that the generation counter matches" -> "the node MUST confirm that the generation counter matches"
• "If it does not match, it is silently dropped." -> "If it does not match, it MUST be silently dropped."

closes deanwillis/p2psip-base-master#158