On success, the number of bytes written should be returned.
Previously `buf.len()` was always returned. The function `send_slice`
> ... returns the amount of octets actually enqueued, which is limited
> by the amount of free space in the transmit buffer; down to zero.
"down to zero" is okay as that is checked by `can_send`.
Signed-off-by: Anhad Singh <andypython@protonmail.com>
Anhad Singh
cdea756569