Function keys in any virtual console create some dump on main
console (first virtual, /dev/console); unless debug_fkeys=0 is set
in boot monitor, in which case no function keys generate dump.
With this patch, you can restrict the virtual console where dumps
are produced; with debug_fkeys=0, none generates dumps (unchanged);
with debug_fkeys=1 (most useful setting), only the first virtual
console, which is the one which gets the dumps, can generate output;
on second and further consoles (/dev/ttyc?), the function keys are
passed to applications.
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