Squashed commit of the following:
net/icmpv6: IPPROT_ICMP6 socket logic now builds without error.
net/icmpv6: Add support for read-ahead and poll(). Initial commit is just cloned from ICMP with the appropriate name changes.
configs/: All defconfig filess that include CONFIG_NET_ICMPv6_SOCKET=y need to select CONFIG_SYSTEM_PING6=y and deselect CONFIG_DISABLE_POLL.
Update NSH documention to show that ping6 is now a built in command.
net/icmpv6: Add icmpv6_sendto.c and icmpv6_recvfrom.c. Initial versions are just clones from icmp/ with appropriate name changes.
net/icmpv6: Clone some ICMP socket logic as the beginning of support for ICMPv6 socket support.
Rename CONFIG_NET_ICMPv6_PING to CONFIG_NET_ICMPv6_SOCKET. Move prototype for icmpv6_ping from include/nuttx/net/icmpv6 to net/icmpv6/icmpv6.h
Squashed commit of the following:
net/icmp: Finishes off icmp_recvfrom().
net/icmp: Add readahead support for IPPROTO_ICMP sockets.
net/icmp: Add poll() support for IPPROTO_ICMP sockets.
net/icmp: Add a connection structure for IPPROTO_ICMP sockets.
net/icmp: Implements sendto for the IPPROTO_ICMP socket.
net/icmp: Move icmp_sendto() and icmp_recvfrom() to separate files. They are likely to be complex (when they are implemented).
net/icmp: Hook IPPROTO_ICMP sockets into network. Fix some naming collisions. Still missing basic ICMP send/receive logic.
configs: apps/system/ping current need poll() enabled.
configs: All defconfig files that use to enable low-level support must now enabled CONFIG_SYSTEM_PING.
net/icmp: Adds basic build framework to support IPPROTO_ICMP sockets.
This commit backs out most of commit b4747286b1. That change was added because sem_wait() would sometimes cause cancellation points inappropriated. But with these recent changes, nxsem_wait() is used instead and it is not a cancellation point.
In the OS, all calls to sem_wait() changed to nxsem_wait(). nxsem_wait() does not return errors via errno so each place where nxsem_wait() is now called must not examine the errno variable.
In all OS functions (not libraries), change sem_wait() to nxsem_wait(). This will prevent the OS from creating bogus cancellation points and from modifying the per-task errno variable.
sched/semaphore: Add the function nxsem_wait(). This is a new internal OS interface. It is functionally equivalent to sem_wait() except that (1) it is not a cancellation point, and (2) it does not set the per-thread errno value on return.
