unit-tests: Export ntru_drbg_create as testable function so no linking is required

This way the plugin does not have to be linked explicitly to the test
runner, which otherwise would require that the plugin is either always
enabled to build the tests or that ifdefs are added to the Makefile.

src/libstrongswan/tests/Makefile.am

@@ -53,5 +53,4 @@ tests_CFLAGS = \
 tests_LDFLAGS = @COVERAGE_LDFLAGS@
 tests_LDADD = \
   $(top_builddir)/src/libstrongswan/libstrongswan.la \
-  $(top_builddir)/src/libstrongswan/plugins/ntru/libstrongswan-ntru.la \
   libtest.la

src/libstrongswan/tests/suites/test_ntru.c

@@ -17,6 +17,10 @@
 
 #include <tests/utils/test_rng.h>
 #include <plugins/ntru/ntru_drbg.h>
+#include <utils/test.h>
+
+IMPORT_FUNCTION_FOR_TESTS(ntru, ntru_drbg_create, ntru_drbg_t*,
+						  u_int32_t strength, chunk_t pers_str, rng_t *entropy)
 
 /**
  * NTRU parameter sets to test