[CRIU] [Kernel] Print the mnt_id in current mount namespace

[Chen, Hu]

From: Chen Hu <hu1.chen at intel.com>

Hi,
    If I dump an Android app with CRIU, I get belwo errors:
    "Can't lookup mount=123 for fd=123 path=/exampe"

    I made some progress after debug:
    All the Android app are forked from the process Zygote and will run in a
    new mount namespace via unshare(CLONE_NEWNS). The files opened or mmaped by
    Zygote before fork() still hold a mnt_id in old mnt namespace. Thus CRIU
    complains "can't lookup mount ..." in current namespace.

    I made a kernel patch to print the the corresponding mnt_id in current
    namespace.

Thanks
Chen Hu