bridge tests: re-enable span test

The root cause of the intermittent span test failures has been
identified as a race between sending the packet and starting the bpf
capture.
This is now resolved, so the test can be re-enabled.

PR: 260461
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit e1274b5b2646a49c1e3efce6c9918c99716d3c07)