drivers/serial/pty.c, serial.c, usbdev/cdcacm.c, include/nuttx/fs/ioctl.h:  Fix FIONWRITE and add FIONSPACE.  All implementations of FIONWRITE were wrong.  FIONWRITE should return the number of bytes waiting in the outgoing send queue, not the free space.  Rather, FIONSPACE should return the free space in the send queue.

configs/stm32f4discovery/canard: Change version to lastet. Need to match change to apps/libcanard/Kconfig

SAM3/4 USB and USBMSC fixes.

This fixes a race condition where the HW fills a FIFO bank while the SW is
busy, resulting in out of sequence USB packets.

The scsi thread was waiting for the wrong condition.

However, this was masked by the fact that the code creating the scsi thread
was also holding usbmsc_scsi_lock(priv) while initializing data, hence this
lock synchronized the scsi thread start with init completion.

Fix STM32 RTC Alarm interrupts.  They were being enabled BEFORE the interrupt system was being initialized.

Back out last RTC alarm changes.  I am mistaken, the interrupts are enabled by stm32[l4]_exti_alarm().

serial.c:  Fix a race condition noted by Stefan Kolb.  Between the test if the TX buffer is full and entering a critical section, bytes may be removed from the TX buffer making the wait unnecessary.  The unnecessary wait is an inefficiency, but not really a problem.  But with USB CDC/ACM it can be a problem because the entire TX buffer may be emptied when we lose the race.  If that happens that uart_putxmitchar() can hang waiting for data to be removed from an empty TX buffer.