resolvconf: fixes for the compatibility interface
    
    Also use compat_main() when called as `resolvconf`, since the interface
    is closer to that of `systemd-resolve`.
    
    Use a heap allocated string to set arg_ifname, since a stack allocated
    one would be lost after the function returns. (This last one broke the
    case where an interface name was suffixed with a dot, such as in
    `resolvconf -a tap0.dhcp`.)
    
    Tested:
      $ build/resolvconf -a nonexistent.abc 
      Unknown interface 'nonexistent': No such device
    
    Fixes #9423.
    
    (cherry picked from commit 5a01b3f35d7b6182c78b6973db8d99bdabd4f9c3)
    
    Resolves: #1835594
    
    patch_name: 0392-resolvconf-fixes-for-the-compatibility-interface.patch
    present_in_specfile: true
    location_in_specfile: 392
    squash_commits: true