selftests/bpf: Create iter_tcp_destroy test program

Prepare for bucket resume tests for established TCP sockets by creating
a program to immediately destroy and remove sockets from the TCP ehash
table, since close() is not deterministic.

Signed-off-by: Jordan Rife <jordan@jrife.io>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>