routing: Enable hash_outbound during nhgrp allocation

Multipath routes can be added via both RTM_F_CREATE and RTM_F_APPEND.
Therefore, it's possible to have mpath routes without calling
add_route_flags_mpath.

Instead of checking V_fib_hash_outbound for every route append,
check it during nhgrp_ctl initialization, which is only called for
the first multipath request per rib_head.

PR:		293136
Reviewed by:	glebius
Tested by:	Marek Zarychta <zarychtam@plan-b.pwste.edu.pl>
Differential Revision:	https://reviews.freebsd.org/D57469

sys/net/route/nhgrp_ctl.c

@@ -505,6 +505,12 @@ nhgrp_alloc(uint32_t fibnum, int family, struct weightened_nhop *wn, int num_nho
 			*perror = ENOMEM;
 			return (NULL);
 		}
+		if (V_fib_hash_outbound == 0) {
+			/* Enable local outbound connections hashing. */
+			if (bootverbose)
+				printf("FIB: enabled flowid calculation for locally-originated packets\n");
+			V_fib_hash_outbound = 1;
+		}
 	}
 
 	/* Sort nexthops & check there are no duplicates */

sys/net/route/route_ctl.c

@@ -876,21 +876,8 @@ add_route_flags_mpath(struct rib_head *rnh, struct rtentry *rt,
 		}
 		return (error);
 	}
-	error = change_route_conditional(rnh, rt, rnd_orig, &rnd_new, rc);
-	if (error != 0)
-		return (error);
 
-	if (V_fib_hash_outbound == 0 && NH_IS_NHGRP(rc->rc_nh_new)) {
-		/*
-		 * First multipath route got installed. Enable local
-		 * outbound connections hashing.
-		 */
-		if (bootverbose)
-			printf("FIB: enabled flowid calculation for locally-originated packets\n");
-		V_fib_hash_outbound = 1;
-	}
-
-	return (0);
+	return (change_route_conditional(rnh, rt, rnd_orig, &rnd_new, rc));
 }
 
 /*