get kdump ifname once in kdump_install_net
    
    Resolves: bz1950932
    Upstream: Fedora
    Conflict: None
    
    commit 97ee5dc64c362cd9eef841378e3d95608f73c72d
    Author: Coiby Xu <coxu@redhat.com>
    Date:   Thu May 6 09:20:26 2021 +0800
    
        get kdump ifname once in kdump_install_net
    
        Signed-off-by: Coiby Xu <coxu@redhat.com>
        Acked-by: Kairui Song <kasong@redhat.com>
    
    Signed-off-by: Coiby Xu <coxu@redhat.com>