net: ipv6: rpl_iptunnel: Fix memory leak in rpl_input

net: ipv6: rpl_iptunnel: Fix memory leak in rpl_input

[ Upstream commit 2c84b0aa28b9e73e8c4b4ce038269469434ae372 ]

Free the skb before returning from rpl_input when skb_cow_head() fails.
Use a "drop" label and goto instructions.

Fixes: a7a29f9c361f ("net: ipv6: add rpl sr tunnel")
Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240911174557.11536-1-justin.iurman@uliege.be
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>