bpf: sockmap, add tests for proto updates replace socket

Add test that replaces the same socket with itself. This exercises a
corner case where old element and new element have the same posck.
Test protocols: TCP, UDP, stream af_unix and dgram af_unix.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/r/20231221232327.43678-6-john.fastabend@gmail.com