signals: introduce kernel_sigaction()

signals: introduce kernel_sigaction()

Now that allow_signal() is really trivial we can unify it with
disallow_signal().  Add the new helper, kernel_sigaction(), and
reimplement allow_signal/disallow_signal as a trivial wrappers.

This saves one EXPORT_SYMBOL() and the new helper can have more users.

Signed-off-by: Oleg Nesterov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Al Viro <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>