LCLS, TS 48.008: add GCR IE encoding/decoding

* add functions to encode Global Call. Ref. from TS 29.205 as 3GPP TS
  48.008 ยง3.2.2.115 information element
* add corresponding tests

Change-Id: I82ce0207dc8de50689a8806c6471ad7fbae6219d
diff --git a/tests/gsm0808/gsm0808_test.ok b/tests/gsm0808/gsm0808_test.ok
index e5833d0..d5857e3 100644
--- a/tests/gsm0808/gsm0808_test.ok
+++ b/tests/gsm0808/gsm0808_test.ok
@@ -22,6 +22,9 @@
 Testing creating Paging Request
 Testing creating DTAP
 Testing prepend DTAP
+Testing Global Call Reference IE encoder...
+	15 bytes added: OK
+	decoded 15 bytes: OK
 test_gsm0808_enc_dec_cell_id_list_lac: encoded: 1a 07 05 01 24 ab cd 56 78 (rc = 9)
 ------- test_cell_id_list_add
      cell_id_list == CGI[0]:{}