Make kmalloc for the send buffer a one time alloc based on the MTU for
a given greybus link.
The write_room for an gb_operation_sync then will be the size of the
buffer we use for a single operation.
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>