Implement Linux module parameters as read-only tunable SYSCTLs.

Bool module parameters are no longer supported, because there is no
equivalent in FreeBSD.

There are two macros available which control the behaviour of the
LinuxKPI module parameters:

• LINUXKPI_PARAM_PARENT allows the consumer to set the SYSCTL parent

where the modules parameters will be created.

• LINUXKPI_PARAM_PREFIX defines a parameter name prefix, which is added to all created module parameters.

Sponsored by: Mellanox Technologies
MFC after: 1 week