net: use WARN() for the WARN_ON in commit 3ee3eb2ac1687

net: use WARN() for the WARN_ON in commit 3ee3eb2ac1687

Commit 3ee3eb2ac1687 (tcp: Try to catch MSG_PEEK bug) added a printk()
to the WARN_ON() that's in tcp.c. This patch changes this combination
to WARN(); the advantage of WARN() is that the printk message shows up
inside the message, so that kerneloops.org will collect the message.

In addition, this gets rid of an extra if() statement.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>