g10: Fix key import statistics.

'transfer_secret_keys' collects statistics on a subkey-basis, while
the other code does not. This leads to inflated numbers when
importing secret keys. E.g. 'count' is incremented by the main
parsing loop in 'import', and again in 'transfer_secret_keys', leading
to a total of 3 if one key with two secret subkeys is imported.

• g10/import.c (import_secret_one): Adjust to the fact that

'transfer_secret_keys' collects subkey statistics.

• tests/openpgp/Makefile.am (TESTS): Add new test.
• tests/openpgp/issue2346.scm: New file.
• tests/openpgp/samplekeys/issue2346.gpg: Likewise.

• GnuPG-bug-id: T2346
• Signed-off-by: Justus Winter <justus@g10code.com>