tcpslice: add recipe under tcpdump

tcpslice is a tool for extracting parts of a tcpdump packet trace,
so put it under tcpdump dir

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>