Reenable vnet tests in CI

After restoring the associated commits the tests can be enabled again.

This reverts commit 711524d961.
This reverts commit c4585b938a.

PR:		263767

tests/sys/common/vnet.subr

@@ -13,10 +13,6 @@ unlist_interface()
 
 vnet_init()
 {
-	if [ "$(atf_config_get ci false)" = "true" ]; then
-		atf_skip "https://bugs.freebsd.org/263767"
-	fi
-
 	if [ "`sysctl -i -n kern.features.vimage`" != 1 ]; then
 		atf_skip "This test requires VIMAGE"
 	fi

tests/sys/netpfil/common/utils.subr

@@ -111,8 +111,6 @@ dummynet_init()
 		atf_skip "This test requires dummynet"
 	fi
 
-	atf_skip "Skip to avoid dummynet_send() panic after interface removal."
-
 	case $firewall in
 	ipfw|pf)
 		# Nothing. This is okay.