libfc, fcoe, bnx2fc: Split fc_disc_init into fc_disc_{init, config}

Split discovery initialization in code that is setup once (fcoe_disc_init)
and code that can be re-configured (fcoe_disc_config).

Signed-off-by: Robert Love <robert.w.love@intel.com>
Tested-by: Jack Morgan <jack.morgan@intel.com>
Reviewed-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>