
Add a small helper for ssh_buffer to ensure that the buffer has a certain amount of space already preallocated. This can be useful in case it is known how much data is going to be added to a buffer, to avoid multiple reallocations. Make use of it in few places in the library. Signed-off-by: Pino Toscano <ptoscano@redhat.com> Reviewed-by: Andreas Schneider <asn@cryptomilk.org>