selftests/bpf: Add start_server_addr helper

selftests/bpf: Add start_server_addr helper

In order to pair up with connect_to_addr(), this patch adds a new helper
start_server_addr(), which is a wrapper of __start_server(). It accepts
an argument 'addr' of 'struct sockaddr_storage' type instead of a string
type argument like start_server(), and a network_helper_opts argument as
the last one.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Link: https://lore.kernel.org/r/2f01d48fa026467926738debe554ac452c19b86f.1713427236.git.tanggeliang@kylinos.cn
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>