[ipsec] Packet Too Big message handling in esp6_ctlinput()

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Dear all:

In line 814 to line 843 in esp6_ctlinput(),

    if (cmd == PRC_MSGSIZE) {
            struct secasvar *sav;
            u_int32_t spi;
            int valid;

            /* check header length before using m_copydata */
            if (m->m_pkthdr.len < off + sizeof (struct esp))
                return;
            m_copydata(m, off + offsetof(struct esp, esp_spi),
                sizeof(u_int32_t), (caddr_t) &spi);
            /*
             * Check to see if we have a valid SA corresponding to
             * the address in the ICMP message payload.
             */
            sav = KEY_ALLOCSA((union sockaddr_union *)sa,
                    IPPROTO_ESP, spi);
            valid = (sav != NULL);
            if (sav)
                KEY_FREESAV(&sav);

            /* XXX Further validation? */

            /*
             * Depending on whether the SA is "valid" and
             * routing table size (mtudisc_{hi,lo}wat), we will:
             * - recalcurate the new MTU and create the
             *   corresponding routing entry, or
             * - ignore the MTU change notification.
             */
            icmp6_mtudisc_update(ip6cp, valid);
        }

I don't know why ESP needs to take care of ICMP Packet Too Big message 
specially since icmp6_mtudisc_update() will be called in 
icmp6_notify_error(),
which will already update the PMTU of the host. I think the codes here 
could be removed.

BR,
Yi-Wen