vsock: Allow retrying on connect() failure

vsock: Allow retrying on connect() failure

sk_err is set when a (connectible) connect() fails. Effectively, this makes
an otherwise still healthy SS_UNCONNECTED socket impossible to use for any
subsequent connection attempts.

Clear sk_err upon trying to establish a connection.

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250128-vsock-transport-vs-autobind-v3-2-1cf57065b770@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>