hubble: Protect ring reader channel with mutex
hubble: Protect ring reader channel with mutex

The NextFollow method writes to `r.followChan` variable concurrently
from a `go func() {..}` statement when the context is cancelled. That
write may be executed concurrently to the other accesses in NextFollow.
This commit fixes that issue by protecting the access with a mutex.

Signed-off-by: Sebastian Wicki <db043b2055cb3a47b2eb0b5aebf4e114a8c24a5a@isovalent.com>

michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium