feat(rss): port IP_BIND_ADDRESS_NO_PORT (bind-then-connect) from upstream cb9b4d4 to FreeBSD 15.0

Defer source port allocation in in_pcbbind/in6_pcbbind when port==0 so
connect() can pick an RSS-aware source port via the R-A
INPLOOKUP_LPORT_RSS_CHECK path. v6 connect outer condition is relaxed
under FSTACK to (in6p_laddr unspec || inp_lport==0) so bind-then-connect
actually enters the RSS branch; the inner in6p_laddr overwrite is now
guarded by IN6_IS_ADDR_UNSPECIFIED to preserve a user-bound v6 address.
All hunks gated by #ifdef/#ifndef FSTACK; FSTACK off retains native
FreeBSD 15.0 semantics (REUSEPORT_LB MPASS at L740 unaffected).
Baseline 13.0 contains none of these three hunks; this is a fresh
addition rather than a missed-port migration.

Author: jfb8856606

freebsd/netinet/in_pcb.c

@@ -736,13 +736,19 @@ in_pcbbind(struct inpcb *inp, struct sockaddr_in *sin, int flags,
 	    &inp->inp_lport, flags, cred);
 	if (error)
 		return (error);
+#ifdef FSTACK
+	if (inp->inp_lport != 0) {
+#endif
 	if (__predict_false((error = in_pcbinshash(inp)) != 0)) {
 		MPASS(inp->inp_socket->so_options & SO_REUSEPORT_LB);
 		inp->inp_laddr.s_addr = INADDR_ANY;
 		inp->inp_lport = 0;
 		inp->inp_flags &= ~INP_BOUNDFIB;
 		return (error);
 	}
+#ifdef FSTACK
+	}
+#endif
 	if (anonport)
 		inp->inp_flags |= INP_ANONPORT;
 	return (0);
@@ -1272,11 +1278,13 @@ in_pcbbind_setup(struct inpcb *inp, struct sockaddr_in *sin, in_addr_t *laddrp,
 	}
 	if (*lportp != 0)
 		lport = *lportp;
+#ifndef FSTACK
 	if (lport == 0) {
 		error = in_pcb_lport(inp, &laddr, &lport, cred, lookupflags);
 		if (error != 0)
 			return (error);
 	}
+#endif
 	*laddrp = laddr.s_addr;
 	*lportp = lport;
 	if ((flags & INPBIND_FIB) != 0)

freebsd/netinet6/in6_pcb.c

@@ -352,12 +352,14 @@ in6_pcbbind(struct inpcb *inp, struct sockaddr_in6 *sin6, int flags,
 	if ((flags & INPBIND_FIB) != 0)
 		inp->inp_flags |= INP_BOUNDFIB;
 	if (lport == 0) {
+#ifndef FSTACK
 		if ((error = in6_pcbsetport(&inp->in6p_laddr, inp, cred)) != 0) {
 			/* Undo an address bind that may have occurred. */
 			inp->inp_flags &= ~INP_BOUNDFIB;
 			inp->in6p_laddr = in6addr_any;
 			return (error);
 		}
+#endif
 	} else {
 		inp->inp_lport = lport;
 		if (in_pcbinshash(inp) != 0) {
@@ -512,7 +514,11 @@ in6_pcbconnect(struct inpcb *inp, struct sockaddr_in6 *sin6, struct ucred *cred,
 	    &laddr6.sin6_addr : &inp->in6p_laddr, inp->inp_lport, 0,
 	    M_NODOM, RT_ALL_FIBS) != NULL)
 		return (EADDRINUSE);
+#ifdef FSTACK
+	if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr) || inp->inp_lport == 0) {
+#else
 	if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) {
+#endif
 		if (inp->inp_lport == 0) {
 			error = in_pcb_lport_dest(inp,
 			    (struct sockaddr *) &laddr6, &inp->inp_lport,
@@ -525,7 +531,8 @@ in6_pcbconnect(struct inpcb *inp, struct sockaddr_in6 *sin6, struct ucred *cred,
 			if (error)
 				return (error);
 		}
-		inp->in6p_laddr = laddr6.sin6_addr;
+		if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
+			inp->in6p_laddr = laddr6.sin6_addr;
 	}
 	inp->in6p_faddr = sin6->sin6_addr;
 	inp->inp_fport = sin6->sin6_port;