auditpipe(4): fix some ioctl arguments in the man page

Fix the argument types for the AUDITPIPE_[GS]ET_PRESELECT_(NA)?FLAGS ioctls.
Also, fix some grammar.

[skip ci]

PR: 226713
Submitted by: aniketp
MFC after: 2 weeks
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15620