lib: fix more format warnings (#637)

The following patch was also neccessary to compile.

* command.c: (config_logmsg_cmd) use "%s" format spec
* if.c: (connected_log) ditto
diff --git a/lib/command.c b/lib/command.c
index 45eb9e3..ebb50b4 100644
--- a/lib/command.c
+++ b/lib/command.c
@@ -3054,7 +3054,7 @@
   if ((level = level_match(argv[0])) == ZLOG_DISABLED)
     return CMD_ERR_NO_MATCH;
 
-  zlog(NULL, level, ((message = argv_concat(argv, argc, 1)) ? message : ""));
+  zlog(NULL, level, "%s", ((message = argv_concat(argv, argc, 1)) ? message : ""));
   if (message)
     XFREE(MTYPE_TMP, message);
   return CMD_SUCCESS;
diff --git a/lib/if.c b/lib/if.c
index e310711..d14cfb9 100644
--- a/lib/if.c
+++ b/lib/if.c
@@ -664,7 +664,7 @@
       strncat (logbuf, inet_ntop (p->family, &p->u.prefix, buf, BUFSIZ),
 	       BUFSIZ - strlen(logbuf));
     }
-  zlog (NULL, LOG_INFO, logbuf);
+  zlog (NULL, LOG_INFO, "%s", logbuf);
 }
 
 /* If two connected address has same prefix return 1. */