RDS: TCP: Reduce code duplication in rds_tcp_reset_callbacks()

Some code duplication in rds_tcp_reset_callbacks() can be avoided
by having the function call rds_tcp_restore_callbacks() and
rds_tcp_set_callbacks().

Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>