A string loader tunable requires setting the len parameter to a nonzero
value, typically the size of the string, to have the flag CTLFLAG_TUN
work correctly [1] [2].
Without this fix security.mac.{biba,lomac}.trusted_interfaces would
have no effect at all.
[1] 3da1cf1e88 Extend the meaning of the CTLFLAG_TUN flag to automatically ...
[2] 6a3287f889 Fix regression issue after r267961. Handle special string case ...
Reviewed by: olce, kib
Fixes: af3b2549c4 Pull in r267961 and r267973 again ...
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D48898
7d4c0fac8c