Use s.c_str() in log messages

Fixes issues with data passed to phosphor::logging::log(entry()).
This is part of a series of commits that resolves openbmc 2905.

Tested: static_assert only

Change-Id: I9fac771f54e4acbec97ce1360c106b6e3eb4fe9d
Signed-off-by: Joseph Reynolds <jrey@us.ibm.com>
diff --git a/transporthandler.cpp b/transporthandler.cpp
index bafeb16..98d9573 100644
--- a/transporthandler.cpp
+++ b/transporthandler.cpp
@@ -877,7 +877,7 @@
                 {
                     log<level::INFO>("Failed to get IP object which matches",
                             entry("INTERFACE=%s", ipmi::network::IP_INTERFACE),
-                            entry("MATCH=%s", ethIp));
+                            entry("MATCH=%s", ethIp.c_str()));
                 }
 
                 auto systemProperties = ipmi::getAllDbusProperties(