posix-stack: signal all errors as failed continuations
posix-stack: signal all errors as failed continuations

Currently, if there is a memory allocation failure during accept it
causes either accept() to throw an exception or return a failed future.
It makes it harder to handle such errors in accept() callers.
This patch changes the code so that all errors during accept are
signaled as a failed futures.

Signed-off-by: Paweł Dziepak <e29bb3265626c60caf76d587cabdfcd8b379ef80@scylladb.com>

cloudius-systems/seastar,syuu1228/seastar,scylladb/seastar,avikivity/seastar,avikivity/seastar,scylladb/seastar,kjniemi/seastar,dreamsxin/seastar,kjniemi/seastar,cloudius-systems/seastar,scylladb/seastar,kjniemi/seastar,cloudius-systems/seastar,dreamsxin/seastar,syuu1228/seastar,syuu1228/seastar,dreamsxin/seastar,avikivity/seastar