Fixes for problems found by Coverity in the apps/ repository:

    nshlib/nsh_parse.c: Avoid truncating the strcmp result into a unsigned char variable.

    nshlib/nsh_netcmds.c: Check for valid hostip before using it.

    nshlib/nsh_ddcmd.c: Fix resouce leak when 'if=' or 'of=' params are repeated in the command line.  For example:

       dd if=/dev/null if=/dev/zero of=/dev/null or
       dd if=/dev/zero of=/dev/zero of=/dev/null