Modify IRC enable code

Modify IRC enable code

The switch statements have been replaced by more effective lookup table,
The extern variables declaration has been removed as it would cause
problems with threadsave code later.

The lookup table array is not exported now and for getting the IRC status
the rpp_irc_status function is used instead of accessing the exported
variables.

There also was an error in rpp_irc_disable function, which was returning
FAILURE in case of success.