client.h: Added NIC_ERROR define

This is the same error defined in the new stdsoap2.h library file.

It will be used to identify the error while making the steps to bind the
client to a specific network device.

Signed-off-by: Erik Alexandre Pucci <eap08@c3sl.ufpr.br>
Acked-by: Ricardo Tavares de Oliveira <rto07@c3sl.ufpr.br>
Signed-off-by: Danilo K. S. Yorinori <danilok@c3sl.ufpr.br>