base: Stabilise pldm_msg_hdr_correlate_response()

Use of pldm_msg_hdr_correlate_response() is demonstrated in the
following patch to pldmd:

https://gerrit.openbmc.org/c/openbmc/pldm/+/66819

Change-Id: I875b2dee5247c986a36ccd456956fb7e2a18d11a
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/src/base.c b/src/base.c
index 39dcd65..908621b 100644
--- a/src/base.c
+++ b/src/base.c
@@ -65,7 +65,7 @@
 	return PLDM_SUCCESS;
 }
 
-LIBPLDM_ABI_TESTING
+LIBPLDM_ABI_STABLE
 bool pldm_msg_hdr_correlate_response(const struct pldm_msg_hdr *req,
 				     const struct pldm_msg_hdr *resp)
 {