Suggested improvement to ZBXNEXT-2072.

Complex macro structures like "{#MACRO_1}.{#MACRO2}" can be used in creation of host prototype host names. 

Please implement the same logic also for custom interface DNS name.

Currently only a single LLD macro is supported in DNS field. All other constructions fail with error "Invalid parameter "/1/interfaces/1/dns": a DNS name is expected." whereas the macros would create a perfectly valid DNS name.