scsi: iscsi_tcp: Check that sock is valid before iscsi_set_param()

In the Linux kernel, the following vulnerability has been resolved:

scsi: iscsi_tcp: Check that sock is valid before iscsi_set_param()

The validity of sock should be checked before assignment to avoid incorrect values. Commit 57569c37f0ad ("scsi: iscsi: iscsi_tcp: Fix null-ptr-deref while calling getpeername()") introduced this change which may lead to inconsistent values of tcp_sw_conn->sendpage and conn->datadgst_en.

Fix the issue by moving the position of the assignment.