ping: allow reading /proc/sys/net/ipv6/conf/all/disable_ipv6

Fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1082190

(cherry picked from commit df4d7cb8da,
 without the test update because test-logprof doesn't exist in 3.x yet)

profiles/apparmor.d/bin.ping

@@ -24,6 +24,7 @@ profile ping /{usr/,}bin/{,iputils-}ping {
 
   /{,usr/}bin/{,iputils-}ping mixr,
   /etc/modules.conf r,
+  @{PROC}/sys/net/ipv6/conf/all/disable_ipv6 r,
 
   # Site-specific additions and overrides. See local/README for details.
   include if exists <local/bin.ping>