Fix static dependency on libprotobuf-cpp-lite-ndk

Soong was adding shared dependency on libprotobuf-cpp-lite-ndk in
addition to the manual static dependency.  This resulted in ODR
issues when libc++.so was loaded through libprotobuf-cpp-lite.so.
Set proto.static: true to tell Soong to use the static dependency.

Test: atest sdkextensions_e2e_tests
Change-Id: I2c9f439b98d277e6b53edd2e309f48aade089c45