hostmot2: bound Ethernet packets and check transfers

[sleepybishop]

Split from #4488 as requested. Checks Ethernet transfer lengths and queue bounds, reserves packet-trailer space, and resets queued reads after send failures. A separate commit removes stale 7i95/7i95T connector assignments without changing the mapping.

Includes reproducible mock-socket tests. Local build, regression, sanitizer and static-analysis checks pass; Mesa hardware validation remains pending.

[BsAtHome]

The test cannot run without a writable RIP source tree. It also includes the raw hm2_eth source and needs to link with hostmot2 code just to build. The construct in the test is fragile and the compile step is not guaranteed to be stable. The compiler flags are also wrong with respect to how the normal code is compiled. There is currently no good way to perform tests like this.

[sleepybishop]

The test cannot run without a writable RIP source tree. It also includes the raw hm2_eth source and needs to link with hostmot2 code just to build. The construct in the test is fragile and the compile step is not guaranteed to be stable. The compiler flags are also wrong with respect to how the normal code is compiled. There is currently no good way to perform tests like this.

Thank you, should I remove them? Given the constraints they are unnecessary bloat.

[BsAtHome]

For inspiration you can take a look at some other tests, like tests/kins-jacobian and tests/kins-frames. They use halcompile to build the test-frame and then run a test with halrun with a .hal file. Tests that use halcompile --install can only run when there is a (writable) source-tree, which is why the skip file tests for doing a build. A test done in this way can also (ab)use the rtapi_app_main() function to perform the test and return a value for success/error of the test.