BUG/MINOR: ssl_ckch: Don't duplicate path when replacing a cert entry

BUG/MINOR: ssl_ckch: Don't duplicate path when replacing a cert entry

When a certificate entry is replaced (via 'set ssl cert' command), the path
is duplicated and used to identify the ongoing transaction. However, if the
same command is repeated, the path is still duplicated but the transaction
is not changed and the duplicated path is not released. Thus there is a
memory leak.

By reviewing the code, it appears there is no reason to duplicate the
path. It is always the path of the old entry. So, a reference on it is now
used. This simplifies the code and this fixes the memory leak.

This patch must be backported as far as 2.2.