Move gethtnamaddr.c to net/ subdirectory.

It may be the better place to stay.

Change-Id: I517cc2769f63e1873191768c4732907c14f2c60e

diff --git a/libc/dns/gethnamaddr.c b/libc/dns/net/gethnamaddr.c
similarity index 100%
rename from libc/dns/gethnamaddr.c
rename to libc/dns/net/gethnamaddr.c