Added missing memory release (#2441, #2450)

src/mme/mme-context.c

@@ -145,6 +145,7 @@ void mme_context_final(void)
     mme_pgw_remove_all();
     mme_csmap_remove_all();
     mme_vlr_remove_all();
+    mme_sgsn_remove_all();
 
     ogs_assert(self.enb_addr_hash);
     ogs_hash_destroy(self.enb_addr_hash);