l2t_seq_next should increase position index

l2t_seq_next should increase position index

BugLink: https://bugs.launchpad.net/bugs/1864904
[ Upstream commit 66018a102f7756cf72db4d2704e1b93969d9d332 ]

if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>