Improve error reporting in pfkey_sa_last_used

[matthew j weaver]

While I hunt for the reason child SAs expiring results in ESRCH during 
pfkey_sa_last_used, this more detailed log message on error is much more 
helpful than the default pretty print of "pfkey_sa_last_used: No such process".

I suspect it's useful to others.

Thank you, all.
matthew weaver

---
Index: pfkey.c
===================================================================
RCS file: /cvs/src/sbin/iked/pfkey.c,v
retrieving revision 1.64
diff -u -p -u -r1.64 pfkey.c
--- pfkey.c     23 Apr 2020 20:17:48 -0000      1.64
+++ pfkey.c     24 May 2020 15:34:39 -0000
@@ -939,7 +939,11 @@ pfkey_sa_last_used(int sd, struct iked_c
        if (msg->sadb_msg_errno != 0) {
                errno = msg->sadb_msg_errno;
                ret = -1;
-               log_warn("%s: message", __func__);
+               log_warn(
+                    "%s: pfkey_write error on spi 0x%08x from %s to %s",
+                   __func__, ntohl(sadb.sadb_sa_spi),
+                   print_host((struct sockaddr *)&ssrc, NULL, 0),
+                   print_host((struct sockaddr *)&sdst, NULL, 0));
                goto done;
        }
        if ((sa_life = pfkey_find_ext(data, n, SADB_X_EXT_LIFETIME_LASTUSE))