[HR] SMF selection (#2194)

SMF selection according to 4.3.2.2.3 of TS23.502.

V-SMF makes discovery in the V-NRF according to V-NSSF.

H-SMF makes discovery in the H-NRF according to H-NSSF.
(The AMF goes through the V-NSSF and forwards the message seeking the NRF to the H-NSSF.)

tests/common/context.c

@@ -1587,6 +1587,7 @@ bson_t *test_db_new_simple(test_ue_t *test_ue)
                             "pre_emption_capability", BCON_INT32(1),
                         "}",
                     "}",
+                    "lbo_roaming_allowed", BCON_BOOL(true),
                 "}", "]",
             "}", "]",
             "security", "{",