Wireshark, Qt5 and El Capitan

[Greg Earle]

I've got a Mac mini running El Capitan 10.11.6.  I've held the OS back 
because I have a FireWire audio interface on it and FireWire is 
deprecated in more recent OSes.

I am having a problem with my Blu-ray player not recognizing NFS shares 
on the same Mac mini.  I went to install Wireshark to debug the NFS 
traffic but it won't install because the current "qt5-qtbase" port is 
only for Sierra or newer:

--
Mac-mini:~ admin$ sudo port install qt5-qtbase
--->  Computing dependencies for qt5-qtbase
--->  Fetching distfiles for qt5-qtbase
Error: qt5-qtbase requires macOS 10.12 or later
Error: Failed to fetch qt5-qtbase: incompatible OS version
Error: See 
/opt/local/var/macports/logs/_private_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_aqua_qt5/qt5-qtbase/main.log 
for details.
Error: Follow https://guide.macports.org/#project.tickets to report a 
bug.
Error: Processing of port qt5-qtbase failed
--

Is there any way to build/install an older Wireshark/Qt5 port combo that 
will still work on El Capitan?

My impression of MacPorts has always been that you can only 
build/install whatever port happens to be installed after you last did a 
"port self update".  I can't really risk going to Sierra and have this 
audio interface stop working.  :-/

		- Greg