fix another bug in the inbound message regulator

The fix 93f8ba20 ("thorium: fix bug in inbound message regulator")
actually introduced a bug. With this bug, the flag
FLAG_REGULATOR_IS_ENABLED is never set to 1.

Link: https://github.com/GeneAssembly/biosal/issues/709
Link: https://github.com/GeneAssembly/biosal/issues/740
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>