added more meaningful exception text

Socket/NetdeviceController.cc

@@ -101,7 +101,7 @@ prefix_ void senf::NetdeviceController::openSocket()
 {
     sockfd_ = ::socket( PF_INET, SOCK_DGRAM, 0);
     if ( sockfd_ < 0)
-        throw SystemException();
+        throw SystemException( "Could not open socket for NetdeviceController");
 }
 
 prefix_ void senf::NetdeviceController::ifrName(ifreq& ifr)
@@ -110,10 +110,10 @@ prefix_ void senf::NetdeviceController::ifrName(ifreq& ifr)
     ::memset( &ifr, 0, sizeof(ifr));
     ifr.ifr_ifindex = ifindex_;
     if ( ::ioctl( sockfd_, SIOCGIFNAME, &ifr ) < 0 )
-        throw SystemException();
+        throw SystemException( 
+        		"NetdeviceController: Could not discover the name of the interface with index ") << ifindex_;
 }
 
-
 prefix_ void senf::NetdeviceController::doIoctl(ifreq& ifr, int request)
     const
 {