zebra: raise the privileges before calling socket()
    
    Because of recent changes when creating AF_NETLINK socket, kernel will
    cache capabilities of the caller and if file descriptor is used or
    otherwise handed to another process it will check that current user has
    necessary capabilities to use the socket. Hence we need to ensure we
    have necessary capabilities when creating the socket and at the time we
    use the socket.
    
    See: http://www.spinics.net/lists/netdev/msg280198.html
    Resolves: #1097684