selftests: net: tcp_mmap: fix SO_RCVLOWAT setting

selftests: net: tcp_mmap: fix SO_RCVLOWAT setting

Since chunk_size is no longer an integer, we can not
use it directly as an argument of setsockopt().

This patch should fix tcp_mmap for Big Endian kernels.

Fixes: 597b01edafac ("selftests: net: avoid ptl lock contention in tcp_mmap")
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Soheil Hassas Yeganeh <[email protected]>
Cc: Arjun Roy <[email protected]>
Acked-by: Soheil Hassas Yeganeh <[email protected]>
Signed-off-by: David S. Miller <[email protected]>