net: neigh: use long type to store jiffies delta

net: neigh: use long type to store jiffies delta

BugLink: https://bugs.launchpad.net/bugs/1863019
[ Upstream commit 9d027e3a83f39b819e908e4e09084277a2e45e95 ]

A difference of two unsigned long needs long storage.

Fixes: c7fb64db001f ("[NETLINK]: Neighbour table configuration and statistics via rtnetlink")
Signed-off-by: Eric Dumazet <edumazet@google.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>