code: func (b bindAddresses) isAvailable(addr tcpip.Address, reuse bool) bool {
  	if addr == anyIPAddress {
  		if len(b) == 0 {
  			return true
  		}
  		if !reuse {
  			return false
  		}
  		for _, n := range b {
  			if !n.reuse {
  				return false
  			}
  		}
  		return true
  	}
  
  	// If all addresses for this portDescriptor are already bound, no
  	// address is available.
  	if n, ok := b[anyIPAddress]; ok {
  		if !reuse {
  			return false
  		}
  		if !n.reuse {
  			return false
  		}
  	}
  
  	if n, ok := b[addr]; ok {
  		if !reuse {
  			return false
  		}
  		return n.reuse
  	}
  	return true
  }
docs: // isAvailable checks whether an IP address is available to bind to.