rilmodem: Re-factor usage of g_ril_send()

Re-factor usage of g_ril_send(), as it now takes a *parcel
as opposed to *data and data_len.  Also removed calls to
parcel_free() and g_ril_print_request*(),as both are now
handled by g_ril_send().  Finally, got rid of unnecessary
local variables for g_ril_send()'s return value, and similar
change for request (id).
plugins: Re-factor ril's usage of g_ril_send().