code: func (c *IPHAConn) readPacket() (*packet, error) {
  	switch c.af() {
  	case syscall.AF_INET:
  		return c.readIPv4Packet()
  	case syscall.AF_INET6:
  		return c.readIPv6Packet()
  	}
  	panic("unreachable")
  }
docs: // readPacket reads a packet from this IPHAConn's recvConn.