pimd: Fix for crash during networking restart

pimd: Fix for crash during networking restart

During vrf delete, the vxlan_info.work_list
linked list was deleted which is a global list
containing the SGs for all the VRFs.

If two vrfs are configured, vrf a and vrf b and
both has SGs assocaited with them which are
inserted in the vxlan_info.work_list. Now if
vrf a is deleted, it deletes the work_list also.
Due to this when any SG add or del comes for vrf b
it tries to access the work_list and crashes.

Fix
Delete the vxlan_info.work_list only when all the
VRFs are terminated and unset the vxlan_info.flags
so if new add cmd comes it re-allocates the work_list.

Signed-off-by: usrivastava-nvidia <usrivastava@nvidia.com>