ipa: Properly parse LV stream of a ID_GET request

For some reason the structure is closer to be a LV (length
and value). The value is actually a tag but it is counted
inside the length. Introduce an overload of the parse function
to provide an offset for the length. This will be taken from
the returned length.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index b0701f8..6f76e5a 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -16,7 +16,7 @@
 endif
 
 utils_utils_test_SOURCES = utils/utils_test.c
-utils_utils_test_LDADD = $(top_builddir)/src/libosmocore.la
+utils_utils_test_LDADD = $(top_builddir)/src/libosmocore.la $(top_builddir)/src/gsm/libosmogsm.la
 
 a5_a5_test_SOURCES = a5/a5_test.c ../src/gsm/a5.c
 a5_a5_test_LDADD = $(top_builddir)/src/libosmocore.la $(top_builddir)/src/gsm/libosmogsm.la