Fix build for devices with MESH as the default network type

[multiplemonomials]

Summary of changes

This is somewhat similar to the fix I had to do for wifi devices a while back. If the default network device is MESH, we need to ensure that Nanostack and the mesh networking drivers are linked in with mbed-netsocket. This also fixes some CMake build issues for nanostack and the mesh networking drivers.

Impact of changes

Migration actions required

Documentation

---

Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

Tested and KW41Z greentea compiles with this PR!

---