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/include/Makefile.am b/include/Makefile.am
index b1a818d..42a2dc2 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -59,6 +59,7 @@
                        osmocom/gsm/mncc.h \
                        osmocom/gsm/prim.h \
                        osmocom/gsm/l1sap.h \
+                       osmocom/gsm/protocol/gsm_03_40.h \
                        osmocom/gsm/protocol/gsm_03_41.h \
                        osmocom/gsm/protocol/gsm_04_08.h \
                        osmocom/gsm/protocol/gsm_04_11.h \