sms: Implement encoding the address as alphanumeric type

The number of digits is the number of used octets times two (two
digits per octet). The result has been successfully dissected by
wireshark. It has not been tested with real phones.
diff --git a/tests/sms/sms_test.ok b/tests/sms/sms_test.ok
index 915a59c..a71567d 100644
--- a/tests/sms/sms_test.ok
+++ b/tests/sms/sms_test.ok
@@ -12,4 +12,10 @@
 Encoding some tests and printing number of septets/octets
 SEPTETS: 8 OCTETS: 7
 Done
+Testing gsm340_gen_oa
+Result: len(12) data(14 81 21 43 65 87 09 21 43 65 87 19 )
+Result: len(12) data(14 a1 21 43 65 87 09 21 43 65 87 19 )
+Result: len(2) data(00 91 )
+Result: len(9) data(0e d0 4f 78 d9 2d 9c 0e 01 )
+Result: len(12) data(14 d0 4f 78 d9 2d 9c 0e c3 e2 31 19 )
 OK