tcp: change type of alive from int to bool

The alive parameter of tcp_orphan_retries, indicates
whether the connection is assumed alive or not.
In the function and all places calling it is used as a boolean value.

Therefore this changes the type of alive to bool in the function
definition and all calling locations.

Since tcp_orphan_tries is a tcp_timer.c local function no change in
any other file or header is necessary.

Signed-off-by: Richard Sailer <richard@weltraumpflege.org>
Signed-off-by: David S. Miller <davem@davemloft.net>