Add netbw option to systat

[hiren panchasara]

On Wed, Jul 2, 2014 at 4:50 PM, Bryan Venteicher
<bryanv at daemoninthecloset.org> wrote:
> Awhile back, DragonlyFlyBSD added a netbw option to systat that I've ported
> to FreeBSD and found handy at various times:
>
>    netbw      Display aggregate and per-connection TCP receive and transmit
>                       rates.  Only active TCP connections are shown.
>
> Leading to output such as:
>
> tcp accepts        connects                 rcv 1.192G snd 15.77K rexmit
>
>   192.168.10.80:22      192.168.10.20:23103 rcv        snd 415.7  [  NTSX ]
>   192.168.10.80:22      192.168.10.20:46560 rcv 19.80M snd 14.47K [  NTSX ]
>   192.168.10.80:22      192.168.10.20:60699 rcv        snd 886.3  [  NTSX ]
>   192.168.10.81:5201    192.168.10.51:60844 rcv 293.2M snd        [R  TSX ]
>   192.168.10.81:5201    192.168.10.51:60845 rcv 293.5M snd        [R  TSX ]
>   192.168.10.81:5201    192.168.10.51:60846 rcv 293.2M snd        [R  TSX ]
>   192.168.10.81:5201    192.168.10.51:60847 rcv 292.9M snd        [R  TSX ]
>
> It uses the sequences number from the 'struct tcpcb' to derive the rates,
> which is usually good but certainly not perfect (i.e., don't set the
> interval too long).
>
> I'd like to commit this if anybody else thinks they'd find it useful.
>
> http://people.freebsd.org/~bryanv/patches/systat-netbw.patch

I like the idea.

A few things about the patch:
1) You may want to remove the code hidden behind "#if 0" at 2 places.
2) I am not entirely clear on why/if we need the last column with
flags but if we keep it (for compatibility of any other reason), It
would be nice to have those flags explained in the manpage:

+ mvwprintw(wnd, LINES-2, 0,
+  "Rate/sec, "
+  "R=rxpend T=txpend N=nodelay T=tstmp "
+  "S=sack X=winscale F=fastrec");
3) I feel that the header line for o/p (specially 'tcp accepts and
connects' terminology) can be improved but I do not have a better
suggestion :-)

It looks okay me otherwise and thanks for your work.

cheers,
Hiren