gpg: Fix mailbox based search via AKL keyserver method.

* g10/keyserver.c (keyserver_import_name): Rename to ...
(keyserver_import_mbox): this.  And use mail search mode.
* g10/getkey.c (get_pubkey_byname): Change the two callers.

In contrast to a search via keyserver_import_ntds the older
keyserver_import_name used a full match of the provided name despite
that it is only called with an addr-spec (mbox). Due to the mode the
pattern send to dirmngr was prefixed with a '=' and thus dirmngr used
an exact search;. This did only work for provided user ids like
"foo@example.org" but not for "<foo@example.org>" or
"Foo <foo@xample.org>". The old code dates back to 2010.

• Signed-off-by: Werner Koch <wk@gnupg.org>