Log pre-handshake packet drops using D_MULTI_DROPPED

Log pre-handshake packet drops using D_MULTI_DROPPED

We have a debug level packets dropped by the TLS layer - use that for this
packet drop too.  This changes this message from 'verb 3' to 'verb 4'
(which should result in less user reports about this almost always
harmless warning).

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20180211101929.4535-1-steffan@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16477.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>