6loWPAN:  Add some checks for the case where there are multiple network devices and multiple link layer protocols.

not a clean fix, but at least makes DHCP working with CONFIG_NETDEV_MULTINIC

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Revert "Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards."

This reverts commit 935cc4e3.

add getpreamblelen
add comments

Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards.

sched: Fix tg_flags check with GROUP_FLAG_NOCLDWAIT

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Jira: PDFW15IS-208
Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

Adds USB host support to stm32f411-disco board.

Approved-by: Gregory Nutt <gnutt@nuttx.org>

TUN driver: Implement TAP (OSI layer 2) mode.

Approved-by: Gregory Nutt <gnutt@nuttx.org>