kernel-pfkey: Add option to set receive buffer size of event socket

If many requests are sent to the kernel the events generated by these
requests may fill the receive buffer before the daemon is able to read
these messages.

Fixes #783.

conf/Makefile.am

@@ -64,6 +64,7 @@ plugins = \
 	plugins/led.opt \
 	plugins/kernel-libipsec.opt \
 	plugins/kernel-netlink.opt \
+	plugins/kernel-pfkey.opt \
 	plugins/kernel-pfroute.opt \
 	plugins/load-tester.opt \
 	plugins/lookip.opt \