isdn: accept CAPI Informational Info values as success

Info values in the 0x00xx range are defined in the CAPI standard
as "Informational, message processed successfully". Therefore a
CONNECT_B3_CONF message with an Info value in that range should
open an NCCI just as with Info==0.

Impact: minor bugfix
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Acked-by: Karsten Keil <keil@b1-systems.de>
Signed-off-by: David S. Miller <davem@davemloft.net>