MINOR: ssl: ckch_conf_cmp() compare multiple ckch_conf structures

MINOR: ssl: ckch_conf_cmp() compare multiple ckch_conf structures

The ckch_conf_cmp() function allow to compare multiple ckch_conf
structures in order to check that multiple usage of the same crt in the
configuration uses the same ckch_conf definition.

A crt-list allows to use "crt-store" keywords that defines a ckch_store,
that can lead to inconsistencies when a crt is called multiple time with
different parameters.

This function compare and dump a list of differences in the err variable
to be output as error.

The variant ckch_conf_cmp_empty() compares the ckch_conf structure to an
empty one, which is useful for bind lines, that are not able to have
crt-store keywords.

These functions are used when a crt-store is already inialized and we
need to verify if the parameters are compatible.

ckch_conf_cmp() handles multiple cases:

- When the previous ckch_conf was declared with CKCH_CONF_SET_EMPTY, we
  can't define any new keyword in the next initialisation
- When the previous ckch_conf was declared with keywords in a crtlist
  (CKCH_CONF_SET_CRTLIST), the next initialisation must have the exact
  same keywords.
- When the previous ckch_conf was declared in a "crt-store"
  (CKCH_CONF_SET_CRTSTORE), the next initialisaton could use no keyword
  at all or the exact same keywords.