Backport the tonga->bifroest move to 0.2.4.

This is a backport of 19728 and 19690

changes/bifroest

@@ -0,0 +1,3 @@
+  o Directory authority changes (also in 0.2.8.7):
+    - The "Tonga" bridge authority has been retired; the new bridge
+      authority is "Bifroest". Closes tickets 19728 and 19690.

src/or/config.c

@@ -794,8 +794,8 @@ add_default_trusted_dir_authorities(dirinfo_type_t type)
       "86.59.21.38:80 847B 1F85 0344 D787 6491 A548 92F9 0493 4E4E B85D",
     "dizum orport=443 v3ident=E8A9C45EDE6D711294FADF8E7951F4DE6CA56B58 "
       "194.109.206.212:80 7EA6 EAD6 FD83 083C 538F 4403 8BBF A077 587D D755",
-    "Tonga orport=443 bridge no-v2 82.94.251.203:80 "
-      "4A0C CD2D DC79 9508 3D73 F5D6 6710 0C8A 5831 F16D",
+    "Bifroest orport=443 bridge no-v2 "
+      "37.218.247.217:80 1D8F 3A91 C37C 5D1C 4C19 B1AD 1D0C FBE8 BF72 D8E1",
     "gabelmoo orport=443 no-v2 "
       "v3ident=ED03BB616EB2F60BEC80151114BB25CEF515B226 "
       "131.188.40.189:80 F204 4413 DAC2 E02E 3D6B CF47 35A1 9BCA 1DE9 7281",