package/libssh2: fix CVE-2019-17498

package/libssh2: fix CVE-2019-17498

In libssh2 v1.9.0 and earlier versions, the SSH_MSG_DISCONNECT logic in
packet.c has an integer overflow in a bounds check, enabling an attacker
to specify an arbitrary (out-of-bounds) offset for a subsequent memory
read. A crafted SSH server may be able to disclose sensitive information
or cause a denial of service condition on the client system when a user
connects to the server.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>