broadband-modem-nokia: N900 doesn't disable echo unless explicitly done

During init, the N900 appears to ignore an E0 in the same command as
an E1.  So just add another init command to disable echo, which won't
have any effect on devices that work with the first command.

plugins/nokia/mm-broadband-modem-nokia.c

@@ -203,6 +203,8 @@ static const gchar *primary_init_sequence[] = {
     /* When initializing a Nokia port, first enable the echo,
      * and then disable it, so that we get it properly disabled. */
     "E1 E0",
+    /* The N900 ignores the E0 when it's on the same line as the E1, so try again */
+    "E0",
     /* Get word responses */
     "V1",
     /* Extended numeric codes */