Apply a workaround for the unkillable jail problem where some devices created within the jail are never freed. si_cred is only used by the MAC framework so make the cred reference conditional on it being compiled in, this is not a fix and will need to be reviewed for any new consumers of si_cred.
Apply a workaround for the unkillable jail problem where some devices created
within the jail are never freed. si_cred is only used by the MAC framework so
make the cred reference conditional on it being compiled in, this is not a fix
and will need to be reviewed for any new consumers of si_cred.

This will quell some user complaint when using jails with a default kernel.

Reviewed by:	rwatson
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase