Unix domain:  With these changes I can build a system with no link layer enabled, only Unix domain sockets

Recent changes to stm32_rtcc.c do not compile with STM32L15XX configurations.  From Jussi Kivilinna.

Disabling any of EXTI 5-9 interrupts was disabling interrupts for all EXTI 5-9. Same issue with EXTI 10-15.  From Jussi Kivilinna.

Get USART 2 & 3 working on lpc4357-evb. These changes are required to get USART 2 and 3 working on the Embest development board.  From Toby Duckworth

Networking:  Move TCP specific logic out of net/socket/accept.c to net/tcp/tcp_accept.c; add hooks for local, Unix doamin sockets

Networking:  Move TCP specific logic out of net/socket/accept.c to net/tcp/tcp_accept.c; add hooks for local, Unix doamin sockets