Trouble with 7bae7c8e and radsec clients causing mutex crash

[Sam Hartman]

I guess a bit less opacity is in order:
>   0xb7f94702 <fr_inaddr_mask+34>:      mov    $0x20,%ecx
>      0xb7f94707 <fr_inaddr_mask+39>:      sub    %edx,%ecx
>         0xb7f94709 <fr_inaddr_mask+41>:      mov    $0xffffffff,%edx
	    0xb7f9470e <fr_inaddr_mask+46>:      shl    %cl,%edx
>	    => 0xb7f94710 <fr_inaddr_mask+48>:      bswap  %edx
>	       0xb7f94712 <fr_inaddr_mask+50>:      and    (%esi),%edx

That's disassembley of the interesting part of fr_inaddr_mask.  $cl
contains 32-prefix, and $edx contains the mask we're going to and
against the address.

>I'm not an expert enough in the C standard to figure out why I get a different answer when I run 
>(gdb) p ~((0x00000001UL << (32 - 0)) - 1)
>$36 = 0

that's running the same expression from the C that generates the
assembley above, with 0 subsubstituted for prefix.
That will have us anding 0 with the address which is what we want.