Fix -B with some SCTP tests, which is part of #678

[jijianwen]

Got the following error when running server side with -B option:

Server side:
./iperf3 -s -B <server_ipv4_address>
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
iperf3: error - unable to start stream listener: Bad file descriptor
-----------------------------------------------------------

Client side:
./iperf3 -c <server_ipv4_address> --sctp
iperf3: error - unable to start stream listener: No such file or directory

Similar fix as below for TCP:
commit eb1cfe5
Author: Bruce A. Mah bmah@es.net
Date: Fri Aug 1 16:24:14 2014 -0700

    Another iteration on issue #193, fixes -B with some TCP tests.

Signed-off-by: Jianwen Ji jijianwen@gmail.com

PLEASE NOTE the following text from the iperf3 license. Submitting a
pull request to the iperf3 repository constitutes "[making]
Enhancements available...publicly":

You are under no obligation whatsoever to provide any bug fixes, patches, or
upgrades to the features, functionality or performance of the source code
("Enhancements") to anyone; however, if you choose to make your Enhancements
available either publicly, or directly to Lawrence Berkeley National
Laboratory, without imposing a separate written license agreement for such
Enhancements, then you hereby grant the following license: a non-exclusive,
royalty-free perpetual license to install, use, modify, prepare derivative
works, incorporate into other computer software, distribute, and sublicense
such enhancements or derivative works thereof, in binary and source code form.

The complete iperf3 license is available in the LICENSE file in the
top directory of the iperf3 source tree.

• Version of iperf3 (or development branch, such as master or
  3.1-STABLE) to which this pull request applies:

• Issues fixed (if any):

• Brief description of code changes (suitable for use as a commit message):

[jijianwen]

@bmah888 , Please help review this patch

[bmah888]

Thanks for taking the time to send this pull request. This is an acknowledgment of having seen it...I'm hoping to find some free cycles to work on iperf3 sometime soon.

[bmah888]

Looks good and seems to fix the problem. Thanks for the pull request!