zcip: allow our own class B range to be used for ZeroConf

zcip: allow our own class B range to be used for ZeroConf

169.254 may already be used by a local network. This patch allows
specifying your own IP range.

Our particular use case is a mesh network, in which the nodes partaking
were using an IP range specifically assigned for the meshing purpose.
As the LAN side of the mesh node could use 169.254, this default range
was not an option.

function                                             old     new   delta
zcip_main                                           1342    1426     +84
pick_nip                                               -      40     +40
packed_usage                                       29974   29969      -5
pick                                                  34       -     -34
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 1/1 up/down: 124/-39)            Total: 85 bytes

Signed-off-by: Michel Stam <m.stam@fugro.nl>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>