指定PING的网卡

 struct ifreq ifr;

 // 绑定在eth0上
 memset( &ifr, , sizeof( struct ifreq ) );
 snprintf( ifr.ifr_name, sizeof( ifr.ifr_name ), "%s", ifname );
 if ( setsockopt( fd, SOL_SOCKET, SO_BINDTODEVICE, ( const void* )&ifr, sizeof( struct ifreq ) ) == - )
 {
     perror( "setsockopt[SO_BINDTODEVICE]" );
     goto err_exit;
 }