kernel: ipcp_select_by_dif: fix selection algorithm
kernel: ipcp_select_by_dif: fix selection algorithm

In case a DIF name is not specified, this takes into account:
    - shim DIFs if no normal DIFs are available
    - normal DIFs with the minimum depth (highest rank)

autrimpo/rlite,autrimpo/rlite,vmaffione/rlite,vmaffione/rlite,vmaffione/rlite,autrimpo/rlite,vmaffione/rlite,autrimpo/rlite