add jhash.h, copied from linux/jhash.h

Allow using arbitrary length data as hashtable key:
Copy jhash.h implementation from the linux kernel.
Apply osmo_ prefix to all global symbols.

Add jhash_test to ensure the code import works as intended.

First application will be a hashtable keyed by umts_cell_id in
osmo-hnbgw.git.

Related: SYS#6773
Change-Id: I0c9652bbc9e2a18b1200e7d63bb6f64ded7d75fa
diff --git a/tests/testsuite.at b/tests/testsuite.at
index e721b93..3433fb0 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -547,3 +547,9 @@
 cat $abs_srcdir/rlp/rlp_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/rlp/rlp_test], [0], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([jhash])
+AT_KEYWORDS([jhash])
+cat $abs_srcdir/jhash/jhash_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/jhash/jhash_test], [0], [expout], [ignore])
+AT_CLEANUP