NOTES: Fix whitespace in "options MAC_DO"

For "options", we put a space before a TAB so that commenting out an
option doesn't move the columns.

No functional change.

Fixes: c8d8cac2a847 ("mac_do(4): allow compiling into kernel")
MFC after: 3 days
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 1cf67b587023af90f2b2c6e87d9103ec42b2b9b2)