I recommend taking a look at LibLog:
It provides a logging abstraction internally to your library without making your library opinionated in the logging framework decision. It "contains transparent built-in support for NLog, Log4Net, EntLib Logging, Serilog, and Loupe, and allows your users to define a custom provider if necessary."
LibLog is a bit more costly performance-wise than calling a logger directly, but in my app profiling, it’s never shown up as a sore spot for me.
Another good option could be Microsoft.Extensions.Logging:
There were some concerns about additional libraries this abstraction pulls in that were not good for library maintainers. I have not evaluated with the new core 2.0 release if this has been resolved yet.