Fix t_net.sh / networking_testdriver after 'broadcast' change

Commit 0df0edc re-introduced explicit setting of broadcast addresses
for Linux IPv4 interfaces.  t_net.sh verifies that the built-in netlink
code (sitnl) achieves the same result as "equivalent" iproute2 statements
- and we missed adjusting of these iproute2 statements (printed by
networking_testdriver).  Done.

Change-Id: I5fea6ca1ccadb434b5c4f4b49881524a079a9d15
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Antonio Quartulli <antonio@mandelbit.com>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1203
Message-Id: <20250922080305.18477-1-gert@greenie.muc.de>
URL: https://sourceforge.net/p/openvpn/mailman/message/59236810/
Signed-off-by: Gert Doering <gert@greenie.muc.de>

Author: cron2

tests/unit_tests/openvpn/test_networking.c

@@ -61,7 +61,7 @@ net__addr_v4_add(const char *addr_str, int prefixlen)
 
     addr = ntohl(addr);
 
-    printf("CMD: ip addr add %s/%d dev %s\n", addr_str, prefixlen, iface);
+    printf("CMD: ip addr add %s/%d dev %s broadcast +\n", addr_str, prefixlen, iface);
 
     return net_addr_v4_add(NULL, iface, &addr, prefixlen);
 }