One of the validation checks for the new array-based TCP SO_REUSEPORT
validation was unintentionally dropped in ea8add2b.  This adds it back.

Lack of this check allows the user to allocate multiple sock_reuseport
structures (leaking all but the first).

Fixes: ea8add2b ("tcp/dccp: better use of ephemeral ports in bind()")
Signed-off-by: Craig Gallek <kraig@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>