selftests/bpf: Support more socket types in create_pair()

Extend the function to allow creating socket pairs of SOCK_STREAM,
SOCK_DGRAM and SOCK_SEQPACKET.

Adapt direct callers and leave further cleanups for the following patch.

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Tested-by: Jakub Sitnicki <jakub@cloudflare.com>
Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://lore.kernel.org/r/20240731-selftest-sockmap-fixes-v2-1-08a0c73abed2@rbox.co


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>