constify map_codec_to_pt() ptmap arg

Change-Id: I030843d2d692b7a73cca8f427df070d2806ab695
diff --git a/include/osmocom/mgcp_client/mgcp_client.h b/include/osmocom/mgcp_client/mgcp_client.h
index ac3e2b1..9b57f10 100644
--- a/include/osmocom/mgcp_client/mgcp_client.h
+++ b/include/osmocom/mgcp_client/mgcp_client.h
@@ -154,7 +154,7 @@
 }
 
 enum mgcp_codecs map_str_to_codec(const char *str);
-unsigned int map_codec_to_pt(struct ptmap *ptmap, unsigned int ptmap_len,
+unsigned int map_codec_to_pt(const struct ptmap *ptmap, unsigned int ptmap_len,
 			     enum mgcp_codecs codec);
 enum mgcp_codecs map_pt_to_codec(struct ptmap *ptmap, unsigned int ptmap_len,
 				 unsigned int pt);
diff --git a/src/libosmo-mgcp-client/mgcp_client.c b/src/libosmo-mgcp-client/mgcp_client.c
index 2dcab62..c28f5d2 100644
--- a/src/libosmo-mgcp-client/mgcp_client.c
+++ b/src/libosmo-mgcp-client/mgcp_client.c
@@ -93,7 +93,7 @@
 }
 
 /* Check the ptmap for illegal mappings */
-static int check_ptmap(struct ptmap *ptmap)
+static int check_ptmap(const struct ptmap *ptmap)
 {
 	/* Check if there are mappings that leave the IANA assigned dynamic
 	 * payload type range. Under normal conditions such mappings should
@@ -122,7 +122,7 @@
  *  \ptmap[in] ptmap_len length of the payload type map.
  *  \ptmap[in] codec the codec for which the payload type should be looked up.
  *  \returns assigned payload type */
-unsigned int map_codec_to_pt(struct ptmap *ptmap, unsigned int ptmap_len,
+unsigned int map_codec_to_pt(const struct ptmap *ptmap, unsigned int ptmap_len,
 			     enum mgcp_codecs codec)
 {
 	unsigned int i;