ipa: rename `struct ipa_link' by `struct ipa_client_link'

And IPA_LINK_STATE_* by IPA_CLIENT_LINK_STATE_* to prepare
the addition of the ipa_server_link abstraction.
diff --git a/src/input/hsl.c b/src/input/hsl.c
index f8c009e..bc8fdb0 100644
--- a/src/input/hsl.c
+++ b/src/input/hsl.c
@@ -302,7 +302,7 @@
         return ret;
 }
 
-static int hsl_bts_process(struct ipa_link *link, struct msgb *msg)
+static int hsl_bts_process(struct ipa_client_link *link, struct msgb *msg)
 {
 	/* XXX: not implemented yet. */
 	return 0;
@@ -333,7 +333,7 @@
 		}
 		break;
 	case E1INP_LINE_R_BTS: {
-		struct ipa_link *link;
+		struct ipa_client_link *link;
 
 		LOGP(DINP, LOGL_NOTICE, "enabling hsl BTS mode\n");