Remove kernel handling of ICMP_SOURCEQUENCH.

It hasn't been used for a very long time.
Additionally, it was deprecated by RFC 6633.

sys/netinet/ip_fastfwd.c

@@ -502,7 +502,6 @@ ip_fastforward(struct mbuf *m)
 	if ((ifp->if_snd.ifq_len + ip_len / ifp->if_mtu + 1) >=
 	    ifp->if_snd.ifq_maxlen) {
 		IPSTAT_INC(ips_odropped);
-		/* would send source quench here but that is depreciated */
 		goto drop;
 	}
 #endif

sys/netinet/ip_icmp.c

@@ -486,12 +486,6 @@ icmp_input(struct mbuf **mp, int *offp, int proto)
 		if (code > 1)
 			goto badcode;
 		code = PRC_PARAMPROB;
-		goto deliver;
-
-	case ICMP_SOURCEQUENCH:
-		if (code)
-			goto badcode;
-		code = PRC_QUENCH;
 	deliver:
 		/*
 		 * Problem with datagram; advise higher level routines.
@@ -670,6 +664,7 @@ icmp_input(struct mbuf **mp, int *offp, int proto)
 	case ICMP_TSTAMPREPLY:
 	case ICMP_IREQREPLY:
 	case ICMP_MASKREPLY:
+	case ICMP_SOURCEQUENCH:
 	default:
 		break;
 	}

sys/netinet/ip_input.c

@@ -104,12 +104,6 @@ SYSCTL_INT(_net_inet_ip, IPCTL_SENDREDIRECTS, redirect, CTLFLAG_VNET | CTLFLAG_R
     &VNET_NAME(ipsendredirects), 0,
     "Enable sending IP redirects");
 
-static VNET_DEFINE(int, ip_sendsourcequench);
-#define	V_ip_sendsourcequench	VNET(ip_sendsourcequench)
-SYSCTL_INT(_net_inet_ip, OID_AUTO, sendsourcequench, CTLFLAG_VNET | CTLFLAG_RW,
-    &VNET_NAME(ip_sendsourcequench), 0,
-    "Enable the transmission of source quench packets");
-
 VNET_DEFINE(int, ip_do_randomid);
 SYSCTL_INT(_net_inet_ip, OID_AUTO, random_id, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(ip_do_randomid), 0,
@@ -1647,25 +1641,6 @@ ip_forward(struct mbuf *m, int srcrt)
 		break;
 
 	case ENOBUFS:
-		/*
-		 * A router should not generate ICMP_SOURCEQUENCH as
-		 * required in RFC1812 Requirements for IP Version 4 Routers.
-		 * Source quench could be a big problem under DoS attacks,
-		 * or if the underlying interface is rate-limited.
-		 * Those who need source quench packets may re-enable them
-		 * via the net.inet.ip.sendsourcequench sysctl.
-		 */
-		if (V_ip_sendsourcequench == 0) {
-			m_freem(mcopy);
-			if (ia != NULL)
-				ifa_free(&ia->ia_ifa);
-			return;
-		} else {
-			type = ICMP_SOURCEQUENCH;
-			code = 0;
-		}
-		break;
-
 	case EACCES:			/* ipfw denied packet */
 		m_freem(mcopy);
 		if (ia != NULL)

sys/netinet/tcp_subr.c

@@ -1429,11 +1429,6 @@ tcp_ctlinput(int cmd, struct sockaddr *sa, void *vip)
 	 */
 	else if (PRC_IS_REDIRECT(cmd))
 		return;
-	/*
-	 * Source quench is depreciated.
-	 */
-	else if (cmd == PRC_QUENCH)
-		return;
 	/*
 	 * Hostdead is ugly because it goes linearly through all PCBs.
 	 * XXX: We never get this from ICMP, otherwise it makes an
@@ -1539,9 +1534,6 @@ tcp6_ctlinput(int cmd, struct sockaddr *sa, void *d)
 	else if (!PRC_IS_REDIRECT(cmd) &&
 		 ((unsigned)cmd >= PRC_NCMDS || inet6ctlerrmap[cmd] == 0))
 		return;
-	/* Source quench is depreciated. */
-	else if (cmd == PRC_QUENCH)
-		return;
 
 	/* if the parameter is from icmp6, decode it. */
 	if (d != NULL) {

sys/sys/protosw.h

@@ -274,8 +274,8 @@ int	pru_sopoll_notsupp(struct socket *so, int events, struct ucred *cred,
 #define	PRC_IFDOWN		0	/* interface transition */
 #define	PRC_ROUTEDEAD		1	/* select new route if possible ??? */
 #define	PRC_IFUP		2	/* interface has come back up */
-#define	PRC_QUENCH2		3	/* DEC congestion bit says slow down */
-#define	PRC_QUENCH		4	/* some one said to slow down */
+/* was	PRC_QUENCH2		3	DEC congestion bit says slow down */
+/* was	PRC_QUENCH		4	Deprecated by RFC 6633 */
 #define	PRC_MSGSIZE		5	/* message size forced drop */
 #define	PRC_HOSTDEAD		6	/* host appears to be down */
 #define	PRC_HOSTUNREACH		7	/* deprecated (use PRC_UNREACH_HOST) */

tools/tools/sysdoc/tunables.mdoc

@@ -1346,15 +1346,6 @@ See
 .Xr inet 4
 for more information.
 
----
-net.inet.ip.sendsourcequench
-bool
-
-This 
-.Nm
-enables or disables the transmission of
-source quench packets.
-
 ---
 net.inet.ip.sourceroute
 bool