move gethost from tools to sendfile01

Move tools/gethost.c to
 testcases/network/tcp_cmds/sendfile/sendfile01_gethost.c
since sendfile01 is the only test that requires gethost.

Signed-off-by: Simon Xu <xu.simon@oracle.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>