ovsdb: Extend maximum JSON string length from 2KiB to 4GiB

In OVS `lib/jsonrpc.c` file, the `jsonrpc_recv()` return `EAGAIN` upon
50 rounds of buffer recv() call. This make it a 2KiB maximum transaction
size. Old code assume that is the maximum size of single JSON string,
this is incorrect, OVS daemon suggest client to try again upon `EAGAIN`
returns.

Unlike OVS `lib/jsonrpc.c` using infinite loop, this patch extend the
maximum JSON string length to 4GiB which should be reasonable enough for
a very long time.

Integration test case included.

Resolves: https://issues.redhat.com/browse/RHEL-121418

Signed-off-by: Gris Ge <fge@redhat.com>