s390: set DHCP client architecure id for netboot

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-parameters

Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Message-Id: <1505126027-1704-1-git-send-email-mihajlov@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>