Revert "Revert "Handle 'sk' being NULL in UID-based routing.""

This reverts commit 7b5be0038765cc41514613d51796b540d55c17b6.
Revert "Revert "net: core: Support UID-based routing.""

This reverts commit 2c7e3ce9ac5a650ad08d49e5390a8f9f8b7ed264.