param: update drivers/char/ipmi/ipmi_watchdog.c to new scheme

param: update drivers/char/ipmi/ipmi_watchdog.c to new scheme

This is one of the most interesting users of module parameters in the
tree, so weaning it off the old-style non-const module_param_call
scheme is a useful exercise.

I was confused by set_param_int/get_param_int (vs. the normal
param_set_int and param_get_int), so I renamed set_param_int to
set_param_timeout, and re-used param_get_int directly instead of
get_param_int.  I also implemented param_check_wdog_ifnum and
param_check_timeout, so now the ifnum_to_use and timeout/pretimeout
parameters can just use plain module_param().

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Corey Minyard <minyard@acm.org>
Cc: openipmi-developer@lists.sourceforge.net