Fix #375, Separate network logic in pc-rtems to support generic targets

[skliper]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fix Separate network logic in pc-rtems to support generic targets #375

NOTE: really this is just a draft proof of concept to show this can be used generically if the network config is removed

Testing performed
Spot checked with LEON3 QEMU.

Expected behavior changes
Eventually plan to use source selection to include platform specific config... or consider making this generic in some other way. PSP module would be nice but I'm not aware of a way to select from a toolchain file or based on platform without making another psp.

System(s) tested on
LEON3 QEMU, see nasa/osal#1350

Additional context
Depends on an as-yet submitted toolchain file.

Third party code
None

Contributor Info - All information REQUIRED for consideration of pull request
Jacob Hageman - NASA/GSFC

[skliper]

@dmknutsen, @alanc98, @jphickey - another one for discussion if we want to go this route or if there are any better ideas

[skliper]

Note - discussed at 20230803 CCB, sounds like this is the right direction just need to separate so the PC specifics can be included in that case (source select)