[ftmod_misdn] Make misdn_handle_mph_information_ind() cope with hfcsusb-style MPH_INFORMATION_IND messages.

Only two mISDN hardware drivers emit MPH_INFORMATION_IND messages and both use a different payload:

	- hfcsusb (HFC-based USB dongle) sends a set of ph_info + ph_info_ch structures
	  which contain the complete state information of the port
	  (including internal hw-specific state and flags).

	- hfcmulti which sends a single integer, a single L1_SIGNAL_* event.

We now try to guess the type of message from the payload length.

The hfcmulti signals are converted to FreeTDM alarm flags; the hfcsusb
state/flags are defined in kernel internal hw-specific headers and are ignored ATM (todo).
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>