fix missing all logging command option

[Pablo Neira Ayuso]

Hi Holger,

Thanks for fixing this, I missed it:

http://cgit.osmocom.org/cgit/libosmocore/commit/?id=952a18ed19f531b82e26108f8c46ef225fddef43

However, this fix is incomplete:

/* This generates the logging command string for VTY. */
const char *log_vty_command_string(const struct log_info *info)
{
        int len = 0, offset = 0, ret, i, rem;
        int size = strlen("logging level () ()") + 1;
                                         ^^
We also have to add `(all|' there.