fnic: Using rport-_dd_data to check rport online instead of rport_lookup

fnic: Using rport-_dd_data to check rport online instead of rport_lookup

From: Satish Kharat <satishkh@cisco.com>

When issuing I/O we check if rport is online through libfc
rport_lookup() function which needs to be protected by mutex lock
that cannot acquired in I/O context. The change is to use midlayer
remote port’s dd_data which is preserved until its devloss timeout
and no protection is required.

Fnic driver version changed from 1.6.0.20 to 1.6.0.21

Signed-off-by: Satish Kharat <satishkh@cisco.com>
Orabug: 22918200
Signed-off-by: Jason Luo <zhangqing.luo@oracle.com>