m4: Put wireshark plugin into epan/ directory

Since wirshark-2.5.0 toplevel plugins are no longer loaded. Only
plugins from epan/, wiretap/ or codecs/ subdirs are. Update the
plugin dir we generate. This is safe to do even for older
wiresharks, since they load plugins from there too.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

libvirt.spec.in

@@ -168,9 +168,9 @@
     %define with_wireshark 0%{!?_without_wireshark:1}
 %endif
 %if 0%{?fedora} || 0%{?rhel} > 7
-    %define wireshark_plugindir %(pkg-config --variable plugindir wireshark)
+    %define wireshark_plugindir %(pkg-config --variable plugindir wireshark)/epan
 %else
-    %define wireshark_plugindir %{_libdir}/wireshark/plugins
+    %define wireshark_plugindir %{_libdir}/wireshark/plugins/epan
 %endif
 
 # Enable libssh transport for new enough distros

m4/virt-wireshark.m4

@@ -50,6 +50,12 @@ AC_DEFUN([LIBVIRT_CHECK_WIRESHARK],[
         dnl time
         ws_plugindir='${exec_prefix}'"${ws_plugindir#$ws_exec_prefix}"
       fi
+
+      dnl Since wireshark 2.5.0 plugins can't live in top level
+      dnl plugindir but have to be under one of ["epan",
+      dnl "wiretap", "codecs"] subdir. The first one looks okay.
+      ws_plugindir="$ws_plugindir/epan"
+
     elif test "x$with_ws_plugindir" = "xno" || test "x$with_ws_plugindir" = "xyes"; then
       AC_MSG_ERROR([ws-plugindir must be used only with valid path])
     else