Rx queues configured with more than 1023 descriptors cause readv() calls to
fail due to more iovec entries than permitted by the kernel. As a result,
no packets can be received.
Quietly limit internal Rx queue size to the maximum number of iovec entries
to fix this issue.
Fixes: 0781f5762cfe ("net/tap: support segmented mbufs")
Signed-off-by: Pascal Mazon <pascal.mazon@6wind.com>