security/logcheck: Miscellaneous changes and cleanups

• Replace deprecated @exec keyword with @postexec in plist.
• Make owner/group/permission of files/directories under ${DATADIR} and ${ETCDIR} same as upstream as much as possible.
• Pet portclippy.
• Reformat Makefile with portfmt.

PR: 257718
MFH: 2021Q3
(cherry picked from commit f026865e514ab4a99cafa63c99439b40f68d0f58)