Bluetooth: Fix l2cap_sock_setsockopt() with optname BT_RCVMTU

Bluetooth: Fix l2cap_sock_setsockopt() with optname BT_RCVMTU

[ Upstream commit 23bc6ab0a0912146fd674a0becc758c3162baabc ]

When we retrieve imtu value from userspace we should use 16 bit pointer
cast instead of 32 as it's defined that way in headers. Fixes setsockopt
calls on big-endian platforms.

Signed-off-by: Amadeusz Sławiński <amadeusz.slawinski@tieto.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>