ircd: s_conf: fix use of strlcpy in strip_tabs

ircd: s_conf: fix use of strlcpy in strip_tabs

strlcpy should be called with the size of the destination buffer, not
the length of the source string.

When the source is an empty string, the destination buffer isn't
written at all, resulting in it trying to output uninitialised data.

This could also cause a buffer overflow on very long invalid config
lines.