cwchar:Use CONFIG_LIBC_WCHAR to only export the wc/mb functions

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

   When a build does not want to use wide or multibyte char
   CONFIG_LIBC_WCHAR is not set. Therefore we should to only
   export the wc/mb functions when defined.

   Regardless of the stat of CONFIG_LIBC_WCHAR the non mb/wc
   definitions such as mbstate_t, wint_t, wctype_t need to be
   exported.

Network routing table:  Trivial name changes to make IPv4 and IPv6 more symmetric.  Add debug logic to dump the content of the router table.

Networking: Fix typo for 802.11 devices in netdev_register().  Was being masked before because depended on CONFIG_NET_MULTLINK.

Fix IPv6 loopback driver that depended on the removed g_ipv6_allonesaddr.  Noted by Masayuki Ishikawa

readme: fix typo Bask->Bash

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

Networking:  Fix netdev_dev_lladdrsize.  In some configurations, it could return the wrong size for the address of a packet radio.

Remove CONFIG_NET_MULTILINK.  This increases code size by a little, but greatly reduces the complexity of the network code.

Remove CONFIG_NETDEV_MULTINIC.  This increases code size by a little, but greatly reduces the complexity of the network code.

libm: Eliminate a warning from lgamma();  Update some comments; Add some logic to handle broadcast better -- Currently conditioned out because it does not work.

ICMPv6: Support source link-layer address option in RA

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

C Coding Standard:  Clarify the form of structures and unions declared with local variable definition.

IPv6:  Remove comparisons to the address with all ones set.  IPv6 does not support broadcast addresses and certainly not in that form.  Replace with multicast addresses beginning with 0xff02.