Add updates noting that the BPF devices and BPF driver might not exist

until you run AIX's tcpdump at least once.

README.aix

@@ -1,11 +1,27 @@
 (1) AIX 4.x's version of BPF is undocumented and somewhat unstandard; the
     current BPF support code includes changes that should work around
-    that, but, lacking an AIX machine on which to compile it, we don't
-    know whether the BPF support for AIX will compile.
-
-    If it doesn't, or if the workarounds fail to make it work correctly,
-    you should send to tcpdump-workers@tcpdump.org a detailed bug report
-    (if the compile fails, send us the compile error messages; if it
+    that; it appears to compile and work on at least one AIX 4.3.3
+    machine.
+
+    Note that the BPF driver and the "/dev/bpf" devices might not exist
+    on your machine; AIX's tcpdump appears to load the driver and create
+    the devices if they don't already exist.  Our libpcap doesn't create
+    them, so you should run (as the super-user) AIX's tcpdump once (you
+    can interrupt it as soon as it starts capturing packets) to create
+    the devices.  Do this before running the configure script, so that
+    the configure script finds the BPF devices and chooses to configure
+    libpcap to use BPF.
+
+    It may be that you will need to do this after every reboot; we don't
+    know whether that's the case, and, if it is the case, don't know
+    whether there's a way to force the driver to be loaded on a reboot. 
+    (We also don't know how to make libpcap create the devices and, if
+    necessary, load the driver.)
+
+(2) If libpcap doesn't compile on your machine when configured to use
+    BPF, or if the workarounds fail to make it work correctly, you
+    should send to tcpdump-workers@tcpdump.org a detailed bug report (if
+    the compile fails, send us the compile error messages; if it
     compiles but fails to work correctly, send us as detailed as
     possible a description of the symptoms, including indications of the
     network link-layer type being wrong or time stamps being wrong).
@@ -22,7 +38,7 @@
 
     to the "configure" script for libpcap.
 
-(2) Also, it is a good idea to have the latest version of the DLPI
+(3) Also, it is a good idea to have the latest version of the DLPI
     driver on your system, since certain versions may be buggy and
     cause your AIX system to crash.  DLPI is included in the
     fileset bos.rte.tty.  I found that the DLPI driver that came with
@@ -37,7 +53,7 @@
 
     These updates can be installed with the smit program.
 
-(3) After compiling libpcap, you need to make sure that the DLPI driver
+(4) After compiling libpcap, you need to make sure that the DLPI driver
     is loaded.  Type:
 
     strload -q -d dlpi