pfctl: Don't use PRIu64

Rather than PRIu64 we can just treat the data as uintmax_t, and use %jx
instead.

MFC after: 1 week
Suggested by: kib
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit 795d78a46713fc16153966e77f20da2f40aac2a3)