telit: optimized supported and current band code

In place of two slightly different regexes for 2g/3g and 2g/3g/4g modems
we now use only one regex with conditional patterns for both supported
and current Bands detection.

Adding also minor fix in test code

plugins/telit/tests/test-mm-modem-helpers-telit.c

@@ -117,7 +117,7 @@ typedef struct {
 static BNDFlagsTest band_flag_test[] = {
     {"0-3", 4, {0, 1, 2, 3} },
     {"0,3", 2, {0, 3} },
-    {"0,2-3,5-7,9", 2, {0, 2, 3, 5, 6, 7, 9} },
+    {"0,2-3,5-7,9", 7, {0, 2, 3, 5, 6, 7, 9} },
     { NULL, 0, {}},
 };