netifd: always send DHCPv4 hostname

udhcpc doesn't send a hostname by default. Use the system hostname if
nothing else is specified, to always send a hostname.

It syncs the behaviour to odhcpc, which always sends a hostname.

Signed-off-by: Mathias Kresin <dev@kresin.me>
Acked-by: Stijn Tintel <stijn@linux-ipv6.be>
Acked-by: Hans Dedecker <dedeckeh@gmail.com>

package/network/config/netifd/files/lib/netifd/proto/dhcp.sh

@@ -40,6 +40,7 @@ proto_dhcp_setup() {
 		append dhcpopts "-x $opt"
 	done
 
+	[ -z "$hostname" ] && hostname="$(cat /proc/sys/kernel/hostname)"
 	[ "$broadcast" = 1 ] && broadcast="-B" || broadcast=
 	[ "$release" = 1 ] && release="-R" || release=
 	[ -n "$clientid" ] && clientid="-x 0x3d:${clientid//:/}" || clientid="-C"