Use tor_addr_from_getsockname() in several places

I'm leaving the getsockname code in transproxy alone, since it is
comparatively isolated, rather platform-specific, and hard to test.

Implements 18105.

changes/18105

@@ -0,0 +1,4 @@
+  o Code simplification and refactoring:
+    - Introduce a function to call getsockname() and return
+      tor_addr_t, to save a little complexity throughout the codebase.
+      Closes ticket 18105.

src/common/address.c

@@ -1672,7 +1672,7 @@ get_interface_address6_via_udp_socket_hack,(int severity,
                                             sa_family_t family,
                                             tor_addr_t *addr))
 {
-  struct sockaddr_storage my_addr, target_addr;
+  struct sockaddr_storage target_addr;
   int sock=-1, r=-1;
   socklen_t addr_len;
 
@@ -1715,21 +1715,19 @@ get_interface_address6_via_udp_socket_hack,(int severity,
     goto err;
   }
 
-  if (tor_getsockname(sock,(struct sockaddr*)&my_addr, &addr_len)) {
+  if (tor_addr_from_getsockname(addr, sock) < 0) {
     int e = tor_socket_errno(sock);
     log_fn(severity, LD_NET, "getsockname() to determine interface failed: %s",
            tor_socket_strerror(e));
     goto err;
   }
 
- if (tor_addr_from_sockaddr(addr, (struct sockaddr*)&my_addr, NULL) == 0) {
-    if (tor_addr_is_loopback(addr) || tor_addr_is_multicast(addr)) {
-      log_fn(severity, LD_NET, "Address that we determined via UDP socket"
-                               " magic is unsuitable for public comms.");
-    } else {
-      r=0;
-    }
- }
+  if (tor_addr_is_loopback(addr) || tor_addr_is_multicast(addr)) {
+    log_fn(severity, LD_NET, "Address that we determined via UDP socket"
+           " magic is unsuitable for public comms.");
+  } else {
+    r=0;
+  }
 
  err:
   if (sock >= 0)

src/common/compat.c

@@ -1402,7 +1402,7 @@ tor_addr_from_getsockname(tor_addr_t *addr_out, tor_socket_t sock)
 {
   struct sockaddr_storage ss;
   socklen_t ss_len = sizeof(ss);
-  memset(ss, 0, sizeof(ss));
+  memset(&ss, 0, sizeof(ss));
 
   if (tor_getsockname(sock, (struct sockaddr *) &ss, &ss_len) < 0)
     return -1;

src/or/connection.c

@@ -1253,15 +1253,12 @@ connection_listener_new(const struct sockaddr *listensockaddr,
       gotPort = usePort;
     } else {
       tor_addr_t addr2;
-      struct sockaddr_storage ss;
-      socklen_t ss_len=sizeof(ss);
-      if (getsockname(s, (struct sockaddr*)&ss, &ss_len)<0) {
+      if (tor_addr_from_getsockname(&addr2, s)<0) {
         log_warn(LD_NET, "getsockname() couldn't learn address for %s: %s",
                  conn_type_to_string(type),
                  tor_socket_strerror(tor_socket_errno(s)));
         gotPort = 0;
       }
-      tor_addr_from_sockaddr(&addr2, (struct sockaddr*)&ss, &gotPort);
     }
 #ifdef HAVE_SYS_UN_H
   /*
@@ -4514,8 +4511,6 @@ alloc_http_authenticator(const char *authenticator)
 static void
 client_check_address_changed(tor_socket_t sock)
 {
-  struct sockaddr_storage out_sockaddr;
-  socklen_t out_addr_len = (socklen_t) sizeof(out_sockaddr);
   tor_addr_t out_addr, iface_addr;
   tor_addr_t **last_interface_ip_ptr;
   sa_family_t family;
@@ -4523,13 +4518,12 @@ client_check_address_changed(tor_socket_t sock)
   if (!outgoing_addrs)
     outgoing_addrs = smartlist_new();
 
-  if (getsockname(sock, (struct sockaddr*)&out_sockaddr, &out_addr_len)<0) {
+  if (tor_addr_from_getsockname(&out_addr, sock) < 0) {
     int e = tor_socket_errno(sock);
     log_warn(LD_NET, "getsockname() to check for address change failed: %s",
              tor_socket_strerror(e));
     return;
   }
-  tor_addr_from_sockaddr(&out_addr, (struct sockaddr*)&out_sockaddr, NULL);
   family = tor_addr_family(&out_addr);
 
   if (family == AF_INET)