Add two missing eventhandler.h headers

These are obviously missing from the .c files, but don't show up in any
tinderbox configuration (due to latent header pollution of some kind).  It
seems some configurations don't have this pollution, and the includes are
obviously missing, so go ahead and add them.

Reported by:	Peter Jeremy <peter AT rulingia.com>
X-MFC-With:	r347984

sys/dev/netmap/netmap_freebsd.c

@@ -32,6 +32,7 @@
 #include <sys/param.h>
 #include <sys/module.h>
 #include <sys/errno.h>
+#include <sys/eventhandler.h>
 #include <sys/jail.h>
 #include <sys/poll.h>  /* POLLIN, POLLOUT */
 #include <sys/kernel.h> /* types used in module initialization */

sys/netinet/netdump/netdump_client.c

@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/conf.h>
 #include <sys/disk.h>
 #include <sys/endian.h>
+#include <sys/eventhandler.h>
 #include <sys/jail.h>
 #include <sys/kernel.h>
 #include <sys/kerneldump.h>