staging: r8188eu: don't accept SIGTERM for cmd thread

staging: r8188eu: don't accept SIGTERM for cmd thread

At the moment, our command thread can be killed by user space.

[root@host ]# kill `pidof RTW_CMD_THREAD`

The driver will then stop working until the module is unloaded
and reloaded.

Don't process SIGTERM in the command thread. Other drivers that have a
command thread don't process SIGTERM either.

Acked-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211016181343.3686-4-martin@kaiser.cx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>