From: Corey Minyard <minyard@acm.org>

I was having a problem with signals with POSIX timers, and it turns out 
that the value of SIGRTMAX is incorrect.  Remember that there is no
signal 0, so the signals should go from 1-_NSIG.  However, SIGRTMAX is
defined as (_NSIG-1) in all architectures.  The following patch fixes this.

This define is only used in drivers/usb/core/devio.c and 
kernel/posix-timers.c, and both are incorrect without this fix.  There's
also no check for zero in posix-timers.c, that fix is part of the diff.

Also, shouldn't do_sigaction() use this value instead of _NSIG?  It's
not a big deal, but some architectures have different values for _NSIG
and SIGRTMAX.