libgcrypt is initialized even for configurations that don't use it

[arader]

• Version of collectd: 5.5.2
• Operating system / distribution: FreeBSD 10.3

Expected behavior

In my configuration I don't enable any crypto for the Network plugin:

<Plugin network>
    Server "10.0.1.21" "8096"
</Plugin>

As such, I expect libgcrypt to not be initialized at all.

Actual behavior

It appears that despite my config libgcrypt is still being initialized. This was discovered because I ran into issue #1870 which was causing collectd to crash.

Steps to reproduce

• Configure collectd's network plugin as above
• Start collectd, notice that libgcrypt is initialized

For more context, see @rubenk's comment here: #1870 (comment)

[octo]

I can confirm that network_init_gcrypt() is called unconditionally from network_init(). I think this call can be removed, because gcrypt is (conditionally) initialized during the configuration phase:

• Both, network_config_add_listen() and network_config_add_server() unconditionally call sockent_init_crypto().
• sockent_init_crypto() calls network_init_gcrypt() only if the socket has security enabled.

The call in network_init() only has any effect, if a server is configured with:

SecurityLevel none
AuthFile "/some/path"

This config does not require clients to encrypt packets, but makes it possible to decrypt packets.

I think we can do the following change:

• Call network_gcrypt_init() from sockent_init_crypto() when a server socket has a non-NULL auth_file (instead of looking at the security level setting). There is a separate check that complains if auth_file is NULL and the security level is not NONE.
• Remove the network_gcrypt_init() call from network_init().