sc_flags assign instead of OR wipes SCF_HASH and negotiated-option flags on TF_NOOPT listener

Summary

After sc->sc_flags=SCF_HASH(:1064) and correct |= additions(SCF_TIMESTAMP:1085,SCF_WINSCALE:1097,SCF_SACK_PERMITTED:1101), code does sc->sc_flags=SCF_NOOPT(:1102-1103) and sc->sc_flags=SCF_SIGNATURE(:1112-1113) — direct assign not |=. Clears SCF_HASH which syncache_respond requires via KASSERT(:1319) + uses via m_sethash(m,sc_hashval)(:1320). DEBUG kernel panics on every SYN to TF_NOOPT listener. Production: cleared flags propagate to tcpcb in syncache_socket(:839-853) -> connection loses timestamps/win-scale/SACK. Fix: use |= not =.