auth.texi (Help for users): Use :port instead of :protocol for all auth-source docs.

auth.texi (Help for users): Use :port instead of :protocol for all auth-source docs.
auth-source.el (auth-source-netrc-parse): Use :port instead of :protocol and accept a missing user, host, or port as a wildcard match.
 (auth-source-netrc-search, auth-source-netrc-create)
 (auth-source-secrets-search, auth-source-secrets-create)
 (auth-source-user-or-password, auth-source-backend, auth-sources)
 (auth-source-backend-parse-parameters, auth-source-search): Use :port instead of :protocol.
nnimap.el (nnimap-credentials): Pass a port default to `auth-source-search' in case an entry needs to be created.
 (nnimap-open-connection-1): Use :port instead of :protocol.