follow_automount() doesn't need the entire nameidata

Only the address of ->total_link_count and the flags.
And fix an off-by-one is ELOOP detection - make it
consistent with symlink following, where we check if
the pre-increment value has reached 40, rather than
check the post-increment one.

[kudos to Christian Brauner for spotted braino]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>