ip_tunnel: Correct spelling in ip_tunnels.h

Correct spelling in ip_tunnels.h
As reported by codespell.

Cc: David Ahern <dsahern@kernel.org>
Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240822-net-spell-v1-3-3a98971ce2d2@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/ip_tunnels.h

@@ -573,7 +573,7 @@ static inline u8 ip_tunnel_get_ttl(const struct iphdr *iph,
 		return 0;
 }
 
-/* Propogate ECN bits out */
+/* Propagate ECN bits out */
 static inline u8 ip_tunnel_ecn_encap(u8 tos, const struct iphdr *iph,
 				     const struct sk_buff *skb)
 {