selftests/bpf: Handle SYSCALL_EPERM and SYSCALL_ENOTSUPP test cases

In preparation to move test cases from bpf/test_sock_addr.c that expect
system calls to return ENOTSUPP or EPERM, this patch propagates errno
from relevant system calls up to test_sock_addr() where the result can
be checked.

Signed-off-by: Jordan Rife <jrife@google.com>
Link: https://lore.kernel.org/r/20240510190246.3247730-6-jrife@google.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>