s390: set DHCP client architecure id for netboot

Setting the client architecture DHCP option to 0x001f (s390 Basic) [1]
allows the DHCP server to return a s390-specific bootfile if wanted.
DHCP servers not configured for the option (or not yet recognizing the
option value) will continue to work as they have done before.

[1] https://www.iana.org/assignments/dhcpv6-parametersSigned-off-by: NViktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Message-Id: <1505126027-1704-1-git-send-email-mihajlov@linux.vnet.ibm.com>
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>

pc-bios/s390-ccw/netboot.mak

@@ -50,7 +50,7 @@ libc.a: $(LIBCOBJS)
 
 LIBNETOBJS := args.o dhcp.o dns.o icmpv6.o ipv6.o tcp.o udp.o bootp.o \
 	      dhcpv6.o ethernet.o ipv4.o ndp.o tftp.o
-LIBNETCFLAGS := $(QEMU_CFLAGS) $(LIBC_INC) $(LIBNET_INC)
+LIBNETCFLAGS := $(QEMU_CFLAGS) -DDHCPARCH=0x1F $(LIBC_INC) $(LIBNET_INC)
 
 %.o : $(SLOF_DIR)/lib/libnet/%.c
 	$(call quiet-command,$(CC) $(LIBNETCFLAGS) -c -o $@ $<,"CC","$(TARGET_DIR)$@")