Implement getInterfaces in util

getInterfaceAddrs returns the map of interface
and associated address,if there is no address
associated with the interface,then we don't get
that interface.
This API gets all the available interfaces on the
system.

Change-Id: I86f07d6e9950a15547cb74356939ca40368bddcc
Signed-off-by: Ratan Gupta <ratagupt@in.ibm.com>
diff --git a/types.hpp b/types.hpp
index e792a3e..4f07522 100644
--- a/types.hpp
+++ b/types.hpp
@@ -7,7 +7,7 @@
 #include <vector>
 #include <map>
 #include <memory>
-
+#include <set>
 #include <systemd/sd-event.h>
 
 namespace phosphor
@@ -61,7 +61,7 @@
 
 using AddrList = std::list<AddrInfo>;
 using IntfAddrMap = std::map<IntfName, AddrList>;
-
+using InterfaceList = std::set<IntfName>;
 
 }//namespace network
 }//namespace phosphor