Add test case for first intermediate max_pathlen=0

!!! This test case is currently failing !!!
(See fix in next-next commit.)

Test certificates generated with the following script:

programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert81.key
programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert82.key
programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert83.key

programs/x509/cert_write serial=81 output_file=cert81.crt is_ca=1 \
    issuer_key=cert81.key issuer_name="CN=Root 8,O=mbed TLS,C=UK" \
    selfsign=1
programs/x509/cert_write serial=82 output_file=cert82.crt is_ca=1 \
    issuer_key=cert81.key issuer_name="CN=Root 8,O=mbed TLS,C=UK" \
    subject_key=cert82.key subject_name="CN=Int 82,O=mbed TLS,C=UK" \
    max_pathlen=0
programs/x509/cert_write serial=83 output_file=cert83.crt \
    issuer_key=cert82.key issuer_name="CN=Int 82,O=mbed TLS,C=UK" \
    subject_key=cert83.key subject_name="CN=EE 83,O=mbed TLS,C=UK"

mv cert8?.crt tests/data_files/dir4
rm cert8?.key
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index a540db2..255c4e1 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -1156,6 +1156,10 @@
 depends_on:POLARSSL_SHA256_C:POLARSSL_RSA_C
 x509_crt_verify_chain:"data_files/dir4/cert61.crt data_files/dir4/cert63.crt data_files/dir4/cert62.crt":"data_files/dir4/cert61.crt":0
 
+X509 CRT verify chain #9 (self signed maxpathlen root)
+depends_on:POLARSSL_SHA256_C:POLARSSL_ECDSA_C:POLARSSL_ECP_DP_SECP256R1_ENABLED
+x509_crt_verify_chain:"data_files/dir4/cert83.crt data_files/dir4/cert82.crt":"data_files/dir4/cert81.crt":0
+
 X509 OID description #1
 x509_oid_desc:"2B06010505070301":"TLS Web Server Authentication"