tun: implement carrier change

tun: implement carrier change

BugLink: https://bugs.launchpad.net/bugs/1806392
The userspace may need to control the carrier state.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Didier Pallard <didier.pallard@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(backported from commit 26d31925cd5ea4b5b168ed538b0326d63ccbb384)
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>