droid4-ngsm ts27010 utility

This program initializes ts27010 line discipline on droid 4 modem uart
and allows typing commands to the ts27010 channels. Eventually other
programs such as ModemManager and ofono can also claim some of the
/dev/gsmtty* ports too hopefully.

At some point n_gsm will probably be initialized by a Linux kernel serdev
driver, so any code using /dev/gsmtty* ports should already assume that
the ports may already be initialized.

This program may add support to proxy some of the ts27010 channels needed
to use the W3GLTE modem in addition to the MDM6600 modem.

For now this program can be just used for typing commands to the mdm6600:

1 AT+CFUN=1
1> U0020AT+CFUN=1
1< U0020+CFUN:OK
...

Where the first number is the dlci channel from 1 to 12 followed by the AT
command to send to mdm6600. Note that the ts27010 AT commands seem to be
Motorola specific while the QMI AT commands are generic. It is unclear at
this point if also QMI commands can be sent over ts27010.

This program can be also used to make a speaker phone test call after
setting alsamixer to "Call" and doing:

$ droid4-ngsm --call=123456789

Then just hit Ctrl-C when done.

To debug what AT commands Android is using, you can do the following:

# echo 0x7fffffff > /sys/module/ts27010mux/parameters/debug_level
# dmesg | grep ts27010 | grep AT
ts27010: >C 3025AT+COPS?
ts27010: >C 3026AT+CREG?
...

Note that with n_gsm you need to use the DLCI numbers, not the device
numbers used by the ts27010 driver. So DLCI 1 means /dev/gsmtty1, while
ts27010 driver uses /dev/mux0 for DLCI1.