L2 VPN encapsulates Ethernet frames by a transport-layer protocol in order to cross an arbitrary network path.
Encapsulating one (or more) Ethernet frame(s) into yet another frame could only tunnel over one L2 network/segment. That wouldn't accomplish much. Also, there's no fragmentation mechanism for Ethernet (or for the data link layer generally).
So, is ...
But how would I set a display filter so it only displays the packet
that has "Broadcast" as their destination port?
There is no broadcast port. Ports are transport protocol addresses, and they are individually assigned to processes.
Broadcast addresses are either IPv4 or data-link addresses. The IPv4 limited broadcast address is 255.255.255.255, ...
What you're looking for is called RSPAN - Remote Switch Port ANalyzer. RSPAN copies frames from a monitored port into a (dedicated) VLAN which you connect to the monitoring station.
Set up a VLAN between the monitored switch and the monitoring station.
Configure RSPAN from the monitored port into the RSPAN VLAN.
I found a detailed description for Brocade ...
This is a better question for a sysadmin section of Stack Exchange, perhaps superuser.
However, on Linux, what you really need is CAP_NET_ADMIN and CAP_NET_RAW which are part of the capabilities system. These can be given to users/programs without running as root; but running them as root is often the simplest way.
You can find a lot more information about ...
Packet capture requires elevated privileges for obvious reasons. (do you want any idiot to be able to watch all traffic?) The program often needs to be able to put the interface in promiscuous mode. And it needs to access a "raw" socket. Both of which are privileged functions.