Fixed incorrect code.

The #endif was misplaced by accident during a refactor:
<029942f4eb>.

clang(1)'s -Wunreachable-code-break (implied by -Weverything) catches
that, but it is only produced for code compiled without support
for Unix sockets, which is probably the reason it was undetected:
no-one seems to be compiling Unit without Unix sockets support (at
least with clang(1)).

src/nxt_sockaddr.c

@@ -208,8 +208,8 @@ nxt_getsockname(nxt_task_t *task, nxt_mp_t *mp, nxt_socket_t s)
 #if (NXT_HAVE_UNIX_DOMAIN)
         case AF_UNIX:
             length = nxt_length("unix:") + socklen;
-#endif
             break;
+#endif
 
         case AF_INET:
             length = NXT_INET_ADDR_STR_LEN;