Add functions for extended RACH coding

Add support for extended RACH (11 bit) according 3GPP TS 45.003 ยง5.3.2:

* convolutional code with puncturing
* encoding/decoding routines
* corresponding tests

Change-Id: I85a34a82d5cd39a594ee89d91a2338226066ab5d
Related: OS#1548
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index a72db52..6e6638a 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -97,6 +97,7 @@
 
 gsm0503_xcch;
 gsm0503_rach;
+gsm0503_rach_ext;
 gsm0503_sch;
 gsm0503_cs2;
 gsm0503_cs3;