docs: Add note about enabling datapath dbg messages
docs: Add note about enabling datapath dbg messages

Add a note to the upgrade guide how to enable datapath debug messages
which were disabled by [1] (released in v1.8.0).

[1]: https://github.com/cilium/cilium/commit/583e67c912e26f7e0bed2656d9ae7544a8d132af

Signed-off-by: Martynas Pumputis <6b0d31c0d563223024da45691584643ac78c96e8@lambda.lt>

tklauser/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,cilium-team/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,cilium-team/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium,tgraf/cilium