monitor: Extract startPerfReaderLocked method
monitor: Extract startPerfReaderLocked method

This commit contains no functional changes and is intended to improve
the readability of subsequent refactoring commits.

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

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