ftmod_libpri: Set default config values, just in case the user forgot to set some parameters in freetdm.conf.xml.

This fixes the "[ERR] ftmod_libpri.c:128 Don't know how to SABME on a type 0 node" messages
from libpri, when there's no "node"/"mode" parameter set for the span.

NOTE: Now defaulting to CPE mode; EuroISDN on BRI/E1 and 4ESS on J1/T1 lines,
      make sure you set dialect/switchtype!
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>