pf: Fix state handling when ICMP packets are diverted

Commit 66f2f1c832 ("pf: handle divert packets") missed a case that I
happened to hit while testing something.

Add a regression test for the ICMP case, based on the existing test.
Fix a buglet in the existing test (missing whitespace after "[").

Reviewed by:	kp
Sponsored by:	OPNsense
Sponsored by:	Klara, Inc.
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D54321

tests/sys/netpfil/pf/divert-to.sh

@@ -402,8 +402,7 @@ pr260867_body()
 	    "pass in on ${epair}b proto tcp from any to port 7 divert-to 0.0.0.0 port 1001"
 
 	reply=$(echo "foo" | nc -N 192.0.2.2 7)
-	if ["${reply}" != "foo" ];
-	then
+	if [ "${reply}" != "foo" ]; then
 		atf_fail "Did not receive echo reply"
 	fi
 }
@@ -413,6 +412,42 @@ pr260867_cleanup()
 	pft_cleanup
 }
 
+atf_test_case "pr260867_icmp" "cleanup"
+pr260867_icmp_head()
+{
+	atf_set descr 'Variant of the PR260867 test'
+	atf_set require.user root
+}
+
+pr260867_icmp_body()
+{
+	pft_init
+	divert_init
+
+	epair=$(vnet_mkepair)
+
+	atf_check ifconfig ${epair}a 192.0.2.1/24 up
+
+	vnet_mkjail alcatraz ${epair}b
+	jexec alcatraz ifconfig ${epair}b 192.0.2.2/24 up
+
+	# Sanity check
+	atf_check -s exit:0 -o ignore ping -c3 192.0.2.2
+
+	jexec alcatraz $(atf_get_srcdir)/../common/divapp 1001 divert-back &
+
+	jexec alcatraz pfctl -e
+	pft_set_rules alcatraz \
+	    "pass in on ${epair}b proto icmp from any to any divert-to 0.0.0.0 port 1001"
+
+	atf_check -o ignore ping -c 3 192.0.2.2
+}
+
+pr260867_icmp_cleanup()
+{
+	pft_cleanup
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case "in_div"
@@ -426,4 +461,5 @@ atf_init_test_cases()
 	atf_add_test_case "in_dn_in_div_in_out_div_out_dn_out"
 
 	atf_add_test_case "pr260867"
+	atf_add_test_case "pr260867_icmp"
 }