sys/socket.h: add SO_BINDTOIFINDEX from linux v5.1

SO_BINDTOIFINDEX behaves similar to SO_BINDTODEVICE, but takes a
network interface index as argument, rather than the network
interface name. see

  linux commit f5dd3d0c9638a9d9a02b5964c4ad636f06cf7e2c
  net: introduce SO_BINDTOIFINDEX sockopt
1 file changed