Remove lowsyslog().  The new syslog() includes all of the functionality of lowsyslog().  No longer any need for two interfaces.

Since syslog_add_intbuffer can now be called from the IDLE thread, it must use a critical section.  Also fix an error in circular buffer index handling.

While working with version 7.10 I discovered a problem in TCP stack that could be observed on high network load. Generally speaking, the problem is that RST flag is set in unnecessary case, in which between loss of some TCP packet and its proper retransmission, another packets had been successfully sent. The scenario is as follows:  NuttX did not receive ACK for some sent packet, so it has been probably lost somewhere. But before its retransmission starts, NuttX is correctly issuing next TCP packets, with sequence numbers increasing properly. When the retransmission of previously lost packet finally succeeds, tcp_input receives the accumulated ACK value, which acknowledges also the packets sent in the meantime (i.e. between unsuccessful sending of lost packet and its proper retransmission). However, variable unackseq is still set to conn->isn + conn->sent, which is truth only if no further packets transmission occurred in the meantime.  Because of incorrect (in such specific case) unackseq value, few lines further condition if (ackseq <= unackseq)is not met, and, as a result, we are going to reset label.

Need to pass va_list as a reference to vsyslog.  This is because va_list is a structure in some compilers and passing of structures in the NuttX sycalls does not work.

There is now one-and-only-one copy of syslog_putc.  It is in the SYSLOG channel logic and can redirect syslog output as needed.  All former syslog_putc versions were renamed and the corresponding SYSLOG device initializaiton now calls syslog_channel()

Some renaming so that future features will fit in better; If the architecture provides its only system logging (via CONFIG_ARCH_SYSLOG), then syslog_initialize() is stubbed out

Move RAMLOG initialize from up_initialilize.c files to syslog_initialize().  up_initialize.c files now call syslog_initialize() unconditionally

Some higher level SYSLOG features are disabled if the architecture-specific logic provides its own SYSLOG functionality

Add a hook before the existing syslog_initialize() call; rename the old syslog_initialize() to syslog_dev_initialize().

Move the OS intensive part of vsyslog and vlowsyslog to drivers/syslog/vsyslog.c and vlowsyslog.c.  Also move lib_syslogstrem to drivers/syslog/syslogstream.c