fib: make sure adj is valid during walk
fib: make sure adj is valid during walk

The adj can be deleted during fib_walk_sync(), make sure it can happen
only after clearing the SYNC_WALK_ACTIVE flag.

Type: fix

Change-Id: I68be00e9602e2783d9dced71c51547c38b7e8a00
Signed-off-by: Benoît Ganne <38aad8ffcfa407b890d258e568f161530f66882d@cisco.com>

chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp