two small changes:

• intercept FIONBIO and FIOASYNC ioctls on netmap file descriptors. libpcap calls them to set non blocking I/O on the file descriptor, for netmap this is a no-op because there is no read/write, but not intercepting would cause fcntl() to return -1
• rate limit and put under netmap.verbose some messages that occur when threads use concurrently the same file descriptor.