Make <sys/ttydefaults.h> more usable.

* TTYDEF_OFLAG referred to the BSD OXTABS constant instead of the Linux XTABS,
  so references to it wouldn't compile.

* CEOL was incorrect (compared to `stty -a`).

* ttydefchars wouldn't compile (removed rather than attempt to fix something
  of unclear utility).

Bug: http://b/63145226
Test: new test
Change-Id: I823e5eaab789cafd2eeea03f77ea553346822f74
diff --git a/tests/Android.bp b/tests/Android.bp
index 2a5b47e..c1dc7ca 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -134,6 +134,7 @@
         "sys_sysmacros_test.cpp",
         "sys_time_test.cpp",
         "sys_timex_test.cpp",
+        "sys_ttydefaults_test.cpp",
         "sys_types_test.cpp",
         "sys_uio_test.cpp",
         "sys_vfs_test.cpp",