sys_util: add more features to UnixSeqpacket
sys_util: add more features to UnixSeqpacket

Add an accept_with_timeout method to UnixSeqpacket and implement a few
basic traits for UnixSeqpacket.

BUG=b:213962590
TEST=cargo test

Change-Id: I1b8461e54aac2be31604213b252c15ce2195e33a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3394438
Reviewed-by: Alexandre Courbot <301cd6a3ea50a894b4b51e385c5eb12b9a4ffc0c@chromium.org>
Reviewed-by: Keiichi Watanabe <815e4e8f7c92a23424d7c3f51ead622bcedbc720@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: David Stevens <2f87ba95ff5d327328bd68c2e86a4d9f2ba99bd0@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm