+/*
+ * Attempt to compress an outgoing TCP packet and return the type of
+ * the result. The caller must have already verified that the protocol
+ * is TCP. The first mbuf must contain the complete IP and TCP headers,
+ * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
+ * compression state, and "compress_cid" tells us whether it is OK
+ * to leave out the CID field when feasible.
+ *
+ * The caller is responsible for adjusting m->m_pkthdr.len upon return,
+ * if m is an M_PKTHDR mbuf.
+ */