fix: lpfc_send_rscn_event sends bigger buffer size

lpfc_send_rscn_event() allocates data for sizeof(struct
lpfc_rscn_event_header) + payload_len, but claims that the data has size
of sizeof(struct lpfc_els_event_header) + payload_len. That leads to
buffer overruns.

Signed-off-by: Ales Novak <alnovak@suse.cz>
Signed-off-by: James Smart <james.smart@avagotech.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sebastian Herbszt <herbszt@gmx.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>