MINOR: tools: extend str2sa_range to add an alt parameter

MINOR: tools: extend str2sa_range to add an alt parameter

Add a new parameter "alt" that will store wether this configuration
use an alternate protocol.

This alt pointer will contain a value that can be transparently
passed to protocol_lookup to obtain an appropriate protocol structure.

This change is needed to allow for example the servers to know if it
need to use an alternate protocol or not.