flow: fix several crash issues

flow: fix several crash issues

Type: fix

This patch fixes crash issues(marked in brackets) in the below test cases

test flow enable index 0 1/1 -> [crash]
test flow disable index 0 1/1 -> [crash]

test flow add src-ip 192.168.8.8 proto udp redirect-to-queue 8
test flow enable index 0 1/1
test flow disable index 0 1/1 - [crash]

test flow add src-ip 192.168.8.8 proto udp redirect-to-queue 8
test flow enable index 0 1/1
test flow enable index 0 1/2
test flow del index 0 -> [crash]

Signed-off-by: Chenmin Sun <chenmin.sun@intel.com>
Change-Id: I84bc6faa3d93a2cab4c82e8a876a8b1067257b62