Add jetpack_top_posts_days filter
Reset to default of 2

1. Cast jetpack_top_posts_days to an int
2. Reset to default of 2
3. Use extra braces

https://github.com/Automattic/Jetpack/pull/37#issuecomment-31369218
Merge pull request #37 from joshbetz/feature-jetpack_top_posts_days-filter

Add jetpack_top_posts_days filter