network: neighbor: Always add neighbors with replace
    
    We were duplicating setting flags for the message and a combination of
    NLM_F_APPEND and NLM_F_CREATE which does not make sense. We should have
    been using NLM_F_REPLACE and NLM_F_CREATE since the kernel can
    dynamically create neighbors prior to us adding an entry. Otherwise, we
    can end up with cases where the message will time out after ~25s even
    though the neighbor still gets added. This delays the rest of the setup
    of the interface even though the error is ultimately ignored.
    
    (cherry picked from commit 192a9d95ea3e058afd824d38a9cea16ad0a84a57)