MFC r327675

pf: Avoid integer overflow issues by using mallocarray() iso. malloc()

pfioctl() handles several ioctl that takes variable length input, these
include:

• DIOCRADDTABLES
• DIOCRDELTABLES
• DIOCRGETTABLES
• DIOCRGETTSTATS
• DIOCRCLRTSTATS
• DIOCRSETTFLAGS

All of them take a pfioc_table struct as input from userland. One of
its elements (pfrio_size) is used in a buffer length calculation.
The calculation contains an integer overflow which if triggered can lead
to out of bound reads and writes later on.

Reported by: Ilja Van Sprundel <ivansprundel@ioactive.com>