Manage Acl For Existing TrafficTable Throwing Exception

Manage Acl For Existing TrafficTable Throwing Exception

Issue Description:
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Elan id may be null, calling the intValue() must throws NPE.

ERROR:
java.lang.NullPointerException: null
    at org.opendaylight.netvirt.aclservice.utils.AclServiceUtils.createCtMarkInstructionForNewState(AclServiceUtils.java:1284)
    at org.opendaylight.netvirt.aclservice.AbstractAclServiceImpl.programAclForExistingTrafficTable(AbstractAclServiceImpl.java:481)

Solution:
================
Determine that the Elan id cannot be null before define ActionNxConntrack

Change-Id: I48a67f75f8ef73c1e44babc324157b9a85560512
Signed-off-by: Ning Zhang <zhangninglc@inspur.com>