This commit adds BBR (Bottleneck Bandwidth and RTT) congestion control.

This is a completely separate TCP stack (tcp_bbr.ko) that will be built only if
you add the make options WITH_EXTRA_TCP_STACKS=1 and also include the option
TCPHPTS.  You can also include the RATELIMIT option if you have a NIC interface
that supports hardware pacing, BBR understands how to use such a feature.

Note that this commit also adds in a general purpose time-filter which
allows you to have a min-filter or max-filter. A filter allows you to
have a low (or high) value for some period of time and degrade slowly
to another value has time passes. You can find out the details of
BBR by looking at the original paper at:

https://queue.acm.org/detail.cfm?id=3022184

or consult many other web resources you can find on the web
referenced by "BBR congestion control". It should be noted that
BBRv1 (which this is) does tend to unfairness in cases of small
buffered paths, and it will usually get less bandwidth in the case
of large BDP paths(when competing with new-reno or cubic flows). BBR
is still an active research area and we do plan on  implementing V2
of BBR to see if it is an improvement over V1.

Sponsored by:	Netflix Inc.
Differential Revision:	https://reviews.freebsd.org/D21582

newlib/libc/sys/rtems/include/netinet/tcp.h

@@ -239,6 +239,7 @@ struct tcphdr {
 #define TCP_BBR_ACK_COMP_ALG   1096 	/* Not used */
 #define TCP_BBR_TMR_PACE_OH    1096	/* Recycled in 4.2 */
 #define TCP_BBR_EXTRA_GAIN     1097
+#define TCP_RACK_DO_DETECTION  1097	/* Recycle of extra gain for rack, attack detection */
 #define TCP_BBR_RACK_RTT_USE   1098	/* what RTT should we use 0, 1, or 2? */
 #define TCP_BBR_RETRAN_WTSO    1099
 #define TCP_DATA_AFTER_CLOSE   1100