Since pr_debug depends on #if DEBUG anyway, there is no need to
contain DEBUGP/pk_debug within a further if. Rename from DEBUGP to
pk_debug, because DEBUGP is flagged by Xtables-addons (- and that's
good so, because often DEBUGPs should have been pr_debug instead).
The printk calls were protected using #if DEBUG anyway, so they can
just be changed to pr_debug. pr_debug also depends on #if DEBUG, and
takes care of the module prefix.
If DEBUG was not defined, and no rule was effectively found, the
"rule" variable may still be non-NULL, and possibly cause deletion.
Therefore, always check for the rule having been found.
