lapdm: Make lapdm_datalink_for_sapi public

This API allows you to get the lapdm_datalink for a SAPI. It's needed in
the lapdm_test, so make it public.
diff --git a/include/osmocom/gsm/lapdm.h b/include/osmocom/gsm/lapdm.h
index a6e4ad7..9393406 100644
--- a/include/osmocom/gsm/lapdm.h
+++ b/include/osmocom/gsm/lapdm.h
@@ -81,6 +81,8 @@
 const char *get_rsl_name(int value);
 extern const char *lapdm_state_names[];
 
+struct lapdm_datalink *lapdm_datalink_for_sapi(struct lapdm_entity *le, uint8_t sapi);
+
 /* initialize a LAPDm entity */
 void lapdm_entity_init(struct lapdm_entity *le, enum lapdm_mode mode, int t200);
 void lapdm_channel_init(struct lapdm_channel *lc, enum lapdm_mode mode);
diff --git a/src/gsm/lapdm.c b/src/gsm/lapdm.c
index 41f4be7..4edae63 100644
--- a/src/gsm/lapdm.c
+++ b/src/gsm/lapdm.c
@@ -181,7 +181,7 @@
 	lapdm_entity_exit(&lc->lapdm_dcch);
 }
 
-static struct lapdm_datalink *datalink_for_sapi(struct lapdm_entity *le, uint8_t sapi)
+struct lapdm_datalink *lapdm_datalink_for_sapi(struct lapdm_entity *le, uint8_t sapi)
 {
 	switch (sapi) {
 	case LAPDm_SAPI_NORMAL:
@@ -543,7 +543,7 @@
 		}
 	}
 
-	mctx.dl = datalink_for_sapi(le, sapi);
+	mctx.dl = lapdm_datalink_for_sapi(le, sapi);
 	/* G.2.1 No action on frames containing an unallocated SAPI. */
 	if (!mctx.dl) {
 		LOGP(DLLAPD, LOGL_NOTICE, "Received frame for unsupported "
@@ -1071,7 +1071,7 @@
 	/* G.2.1 No action shall be taken on frames containing an unallocated
 	 * SAPI.
 	 */
-	dl = datalink_for_sapi(le, sapi);
+	dl = lapdm_datalink_for_sapi(le, sapi);
 	if (!dl) {
 		LOGP(DLLAPD, LOGL_ERROR, "No instance for SAPI %d!\n", sapi);
 		msgb_free(msg);
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 9d15d66..3c5025d 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -172,6 +172,7 @@
 lapdm_channel_set_l1;
 lapdm_channel_set_l3;
 lapdm_channel_set_mode;
+lapdm_datalink_for_sapi;
 lapdm_entity_exit;
 lapdm_entity_init;
 lapdm_entity_reset;