kernel/network: Fix neighbor advertisement hoplimit

All neighbor discovery messages need to be sent with a hop limit of
255, but some messages, like solicited neighbor advertisements, are
unicast messages. So need to set the hop limit for both multicast and
unicast messages.

Fixes #14562

Change-Id: I84fba8acbb5833c65d6113c8a7e0cc821a706881
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6038
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

src/add-ons/kernel/network/datalink_protocols/ipv6_datagram/ipv6_datagram.cpp

@@ -405,6 +405,8 @@ ndp_init()
 	int value = 255;
 	sIPv6Module->setsockopt(sIPv6Protocol, IPPROTO_IPV6, IPV6_MULTICAST_HOPS,
 		&value, sizeof(value));
+	sIPv6Module->setsockopt(sIPv6Protocol, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
+		&value, sizeof(value));
 
 	mutex_init(&sCacheLock, "ndp cache");