common: Provide some convenient OpenPGP related constants.
* common/openpgpdefs.h (OPENPGP_MAX_NPKEY): New. (OPENPGP_MAX_NSKEY): New. (OPENPGP_MAX_NSIG): New. (OPENPGP_MAX_NENC): New. * g10/packet.h: Define PUBKEY_MAX using the new consts.
- Signed-off-by: Werner Koch <wk@gnupg.org>