[SCSI] qla2xxx: Process DPC requests within valid Fabric topologies.

If vports are created and topology is changed to Loop only, the
driver continuously gets a LIP reset occurred and keeps trying to
enable the vport.  Only manage requests during F_Port.

Signed-off-by: Lalit Chandivade <lalit.chandivade@qlogic.com>
Signed-off-by: Giridhar Malavali <giridhar.malavali@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>