The value stored in pf_mtag->tag comes from "tag" and "match tag" keywords in pf.conf and must not be abused for storing other information. A ruleset with enough tags could set or remove the bits responsible for PF_TAG_SYNCOOKIE_RECREATED. Move this syncookie status to pf_mtag->flags. Rename this and other related constants in a way that will prevent such mistakes in the future. Move PF_REASSEMBLED constant to mbuf.h and rename accordingly because it's not a flag stored in pf_mtag, but an identifier of a different m_tag. Change the value of the constant to avoid conflicts with other m_tags using MTAG_ABI_COMPAT. Rename the variables in pf_build_tcp() and pf_send_tcp() in to reduce confusion.

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