sm: Improve the octet string cramming for pkcs#12

* sm/minip12.c (need_octet_string_cramming): New.
(tlv_expect_object, tlv_expect_octet_string): Run the test before
cramming.

* sm/minip12.c (ENABLE_DER_STRUCT_DUMPING): New but undefined macro
for debug purposes.
(bag_decrypted_data_p, bag_data_p): Use macro to allow dumping.
--

This bug was exhibited by importing a gpgsm exported EC certificate.

We use an extra test instead of retrying to allow retruning an error
from malloc failure.  And well, for easier reading of the code.

GnuPG-bug-id: 6536

tests/cms/samplekeys/Description-p12

@@ -1,4 +1,6 @@
 # Description-p12  - Machine readable description of our P12 test vectors
+# The Cert line gives the SHA1 fingerprint of the certificate
+# The Key line gives a hash of the key parameters as returned by minip12.c
 
 Name: ov-user.p12
 Desc: Private test key from www.openvalidation.org
@@ -30,3 +32,11 @@ Desc: QuaVadis format of t5793-openssl
 Pass: test
 Cert: 80348a438e4b803b99e708da0b7fdd0659dedd15
 Key:  c271e44ab4fb19ca1aae71102ea4d7292ccc981d
+
+Name: edward.tester@demo.gnupg.com.p12
+Desc: GnuPG exported Brainpool certificate
+Pass: abc,123456
+Cert: ff810b9281a43c394aa138e9c7fd4c0193216fa6
+Key:  94c6d0b067370a8f2a09ae43cfe8d700bbd61e75
+
+# eof #