Noise reduction in exim4 profile

exim4 profile access to /proc/sys/net/ipv6/conf/all/disable_ipv6
in read mode searching information over IPv6 connection in the host.

In the actual profile this access is denied, this change fix this
and reduce noise in log.

apparmor.d/profiles-a-f/exim4

@@ -55,5 +55,7 @@ profile exim4 @{exec_path} {
         @{run}/exim4/ r,
   owner @{run}/exim4/exim.pid rw,
 
+  @{PROC}/sys/net/ipv6/conf/all/disable_ipv6 r,
+
   include if exists <local/exim4>
 }