Minor changes to fix Patch request in PLDM BIOS test

Changes:
    - Added code to take session

Tested:
   - Ran test suite pldm/test_pldm_bios.robot

Change-Id: Icd4f2a78ff271d3530a671140d3d3cf442a5ed18
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/pldm/test_pldm_bios.robot b/pldm/test_pldm_bios.robot
index 1135dd3..b5d0a4c 100755
--- a/pldm/test_pldm_bios.robot
+++ b/pldm/test_pldm_bios.robot
@@ -135,5 +135,6 @@
 Set Time To Manual Mode
     [Documentation]  Set date time to manual mode via Redfish.
 
+    Redfish.Login
     Redfish.Patch  ${REDFISH_NW_PROTOCOL_URI}  body={'NTP':{'ProtocolEnabled': ${False}}}
     ...  valid_status_codes=[${HTTP_OK}, ${HTTP_NO_CONTENT}]