This is a continuation of ZBX-4148. Some TLS-specific details are still exposed and TLS library headers are still included in src/libs/zbxcrypto/tls.h, which in it's turn is included in many other parts of Zabbix. typedef struct ... ZBX_THREAD_SENDVAL_TLS_ARGS; should be made opaque to avoid that.

Also, there is only one src/libs/zbxcrypto/tls.c and three header files. And none of them is delegated to include/ directory.

I would suggest splitting tls.c into three-four parts according to headers (parameter validation, TLS library initialization, TCP part...) and moving headers to include/.