<arpa/nameser.h>: fix INTRODUCED_IN API level.

Historical research (see bug) suggests that these functions were all in
22. The map file believed this with one (presumably typoed) exception,
but the header file didn't match the map file. It looks like the map was
correct (modulo the one typo), so fix up all the disagreement.

Bug: http://b/113618851
Test: treehugger
Change-Id: Ia579f4e6163206abfac79aa54dc98c792f00ee86
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index b36ee4c..424c8f3 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -690,7 +690,7 @@
     ns_name_ntol; # arm64 x86_64 mips64 introduced=22
     ns_name_ntop; # arm64 x86_64 mips64 introduced=22
     ns_name_pack; # arm64 x86_64 mips64 introduced=22
-    ns_name_pton; # arm64 x86_64 mips64 introduced=23
+    ns_name_pton; # arm64 x86_64 mips64 introduced=22
     ns_name_rollback; # arm64 x86_64 mips64 introduced=22
     ns_name_skip; # arm64 x86_64 mips64 introduced=22
     ns_name_uncompress; # arm64 x86_64 mips64 introduced=22