LU-9859 libcfs: improve API and implementation of blocking signals.

LU-9859 libcfs: improve API and implementation of blocking signals.

According to comment for set_current_blocked() in
kernel/signal.c, changing ->blocked directly is wrong.
sigprocmask() should be called instead.

So change cfs_block_sigsinv() and cfs_restore_sigs()
to use sigprocmask().
For consistency, change them to pass the sigset_t by reference
rather than by value.

Also fix cfs_block_sigsinv() so that it correctly blocks
signals above 32 on a 32bit host.

Linux-commit: 84e07b9d0ac8728b1865b23498d746861a8ab4c2

Change-Id: Iffb8b39ee2b988e9909ceaaba50446eecdf7f249
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-on: https://review.whamcloud.com/35411
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>