ses: minor cleanup

• Prefer variables of small scope rather than large scope
• Remove a magic number
• style(9) for return statements
• Remove the get_enc_status method, which never did anything
• Fix a variable type in the handle_string method
• Proofread some comments

MFC after: 2 weeks
Sponsored by: Spectra Logic, Axcient
Reviewed by: ken, mav
Differential Revision: https://reviews.freebsd.org/D31686