[Thread] add aconfig_declarations for Thread module API flags

This is required to included Thread module APIs in DP2 release.
See ag/26286387

merged-in is used to stop the CL from being merged into U branches

Bug: 325886480
Merged-In: I1eed7982b40d28947aa3f9575c568eac325dc832
Merged-In: I79be1b48058ce6fb08149e18cdd7a5f5b0762769
Change-Id: I79be1b48058ce6fb08149e18cdd7a5f5b0762769
1 file changed