net: tunnel: add pskb_inet_may_pull_reason() helper

[ Upstream commit 7f20dbd7 ]

Introduce the function pskb_inet_may_pull_reason() and make
pskb_inet_may_pull a simple inline call to it. The drop reasons of it just
come from pskb_may_pull_reason().

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 6ead3814 ("vxlan: Fix NPD when refreshing an FDB entry with a nexthop object")
Signed-off-by: Sasha Levin <sashal@kernel.org>