tests/sys/netpfil/pf: Add missing python3 requirements

This also fixes a typo in the dup test that caused the head function to
not be called. On my test system without python3 the tests are now
skipped instead of failing.

Reviewed By:	kp
Differential Revision: https://reviews.freebsd.org/D28903

tests/sys/netpfil/pf/checksum.sh

@@ -32,6 +32,7 @@ unaligned_head()
 {
 	atf_set descr 'Test unaligned checksum updates'
 	atf_set require.user root
+	atf_set require.progs scapy
 }
 
 unaligned_body()

tests/sys/netpfil/pf/dup.sh

@@ -30,10 +30,11 @@
 common_dir=$(atf_get_srcdir)/../common
 
 atf_test_case "dup_to" "cleanup"
-do_to_head()
+dup_to_head()
 {
 	atf_set descr 'dup-to test'
 	atf_set require.user root
+	atf_set require.progs scapy
 }
 
 dup_to_body()