Map umac_ctx struct name too.

Prevents size mismatch linker warnings on Solaris 11.
diff --git a/Makefile.in b/Makefile.in
index 141608b..7f804f5 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -223,7 +223,7 @@
 	$(CC) $(CFLAGS) $(CPPFLAGS) -o umac128.o -c $(srcdir)/umac.c \
 	    -DUMAC_OUTPUT_LEN=16 -Dumac_new=umac128_new \
 	    -Dumac_update=umac128_update -Dumac_final=umac128_final \
-	    -Dumac_delete=umac128_delete
+	    -Dumac_delete=umac128_delete -Dumac_ctx=umac128_ctx
 
 clean:	regressclean
 	rm -f *.o *.a $(TARGETS) logintest config.cache config.log