Use %m over strerror(errno) where possible

Use %m over strerror(errno) where possible

The manual page of strerror() outlines a number of caveats wrt its usage.
Swap for the GNU specific %m printf modifier (also supported on musl and
bionic), which side-steps the issues as much as possible.

Co-authored-by: Cristian Rodríguez <cristian@rodriguez.im>
[emil: split from larger patch, convert more instances to %m]
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/346
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>