usb: change LIST to SLIST to avoid LinuxKPI conflicts

[bz]

Summary

In order to better integrate modern LinuxKPI USB this tries to reduce
a contention point of "LIST". Given there is no need to us a LIST here
change it to SLIST to avoid conflicts.

Sponsored by: The FreeBSD Foundation
X-MFC? unclear

Test Plan

Manually extract from a larger change in a different branch;
make universe for amd64/arm64 are running.

[emaste]

I think this is fine even if it's sort of a lucky workaround (we still mix Linux and FreeBSD namespaces, we're just capitalizing on Linux's lack of SLIST it seems).

sys/dev/usb/usb_device.c

2269

extra blank line?