Partially revert documentated added in 0c4d599 to reflect reality. (#866)

The bug reported in #505 seems to not exist at this time, and
the text added in this manpage change caused some other problems,
a la perfsonar/pscheduler#819.

Fixes #860.

src/iperf3.1

@@ -139,8 +139,6 @@ CPUs).
 .TP
 .BR -B ", " --bind " \fIhost\fR"
 bind to the specific interface associated with address \fIhost\fR.
-If the host has multiple interfaces, it will use the first interface
-by default.
 .TP
 .BR -V ", " --verbose " "
 give more detailed output