sendfile():  Fix error introduced with commit ff73be87.  Noted by Maciej Wójcik

stm32f33xxx: Add HRTIM header file

Approved-by: Gregory Nutt

typos

Approved-by: Gregory Nutt

STM32F33XX DAC, OPAMP, COMP and ADC headers

Approved-by: Gregory Nutt

net/drivers/skeleton.c:  Back out serialization changes of the last commit.  They are not necessary in the skeleton.c example because the calls to net_lock() at the beginning of each worker function will enforce serialization.

drivers/net:  Add framework for serialization in the case where multiple low-priority work queues are used.

Revert "FS:  Fix backward conditional logic that prevent unlink() from building in some configurations."

Oops.  It was not backward.  Enable == !Disable.  Negative logic is confusing.

This reverts commit 1fcf353e.

fixed a typo

Approved-by: Gregory Nutt

Experimental change to STM32 Ethernet driver a success.  Porting change to all other Ethernet drivers.