gsm0808: make gsm0808_create_reset_ack() accessible

The create function to generate the RESET ACKNOWLEDGE
message is not accessible from outside, as it does not
appear in limosmogsm.map. It also has not testcase.

This commit adds gsm0808_create_reset_ack() to the
map file and also adds a testcase.

Change-Id: I82d3411484f82b4a9205d407fa0442244678f183
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index a4e6083..c825dd5 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -141,6 +141,7 @@
 gsm0808_create_layer3;
 gsm0808_create_layer3_aoip;
 gsm0808_create_reset;
+gsm0808_create_reset_ack;
 gsm0808_create_sapi_reject;
 gsm0808_prepend_dtap_header;
 gsm0808_enc_aoip_trasp_addr;