Also rate limit the sending of RST segments in the following cases:
- when receiving data on a closed socket.
- when a socket can not be created at the end of the handshake and the sysctl-variable net.inet.tcp.syncache.rst_on_sock_fail is 1.
- when an ACK segment is received in SYN SENT state and it does not acknowledge the SYN segment.
After this change, there is no need anymore to provide a rstreason to tcp_dropwithreset(), since it is always BANDLIM_TCP_RST. This will be a follow-up commit, since it will change the code in a couple of places, but will not change the functionality. So the functional change can be reviewed here.