nspawn: beef up netns checking a bit, for compat with old kernels
Fixes: #10544
Cherry-picked from: 6619ad889da260cf83079cc74a85d571acd1df5a
patch_name: 0055-nspawn-beef-up-netns-checking-a-bit-for-compat-with-.patch
present_in_specfile: true
location_in_specfile: 55
squash_commits: true