NFLOG: Use correct AF code points on all OSes.

NFLOG: Use correct AF code points on all OSes.

On Haiku R1/beta4 "make check" failed the "nglog-e" test case because
the printer did not recognize address family 2 as IPv4:

-    1  18:31:59.615994 version 0, resource ID 20, family IPv4 (2),
+    1  18:31:59.615994 version 0, resource ID 20, family Unknown (2),

Fix print-nflog.c to use the wire encoding AF code points rather than
the OS libc AF constants.  This fixes "make check" on Haiku and likely
fixes IPv6 NFLOG decoding on a few non-Linux OSes.