rilmodem: re-factor cb_new_data() function.

The cb_new_data() function originally had two parameters used
to initialize the new struct.  Most of our code additionally
uses the cb's user field, and would set it a couple of lines after
the call to cb_new_data().  This change cleans things up a bit.
plugins/ril: re-factor cb_new_data() function.

The cb_new_data() function originally had two parameters used
to initialize the new struct.  Most of our code additionally
uses the cb's user field, and would set it a couple of lines after
the call to cb_new_data().  This change cleans things up a bit.
Merge pull request #18 from tonyespy/cb_data_new

Re-factor cb_data_new() function