pf: use M_WAITOK where possible

In the ioctl path use M_WAITOK allocations whereever possible. These are
less sensitive to memory pressure, and ioctl requests have no hard
deadlines.

Reviewed by: donner
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D30702