fping double call

Steps to reproduce:
Begin from fping version 4.0 - binaries fping and fping6 are the same and logic based on fping v3.x behavior is not optimal in case of ipv6 and without configured source ip. The logic makes double call to fping.

if (0 != (fping_existence & FPING_EXISTS))
	offset += zbx_snprintf(tmp + offset, sizeof(tmp) - offset,
			"%s %s 2>&1 <%s;", CONFIG_FPING_LOCATION, params, filename);

if (0 != (fping_existence & FPING6_EXISTS))
	zbx_snprintf(tmp + offset, sizeof(tmp) - offset,
			"%s %s 2>&1 <%s;", CONFIG_FPING6_LOCATION, params6, filename);

Result:
The do_ping() performance for ipv6 case in 2 times worse

Expected:
Detect fping ipv6 support and do not make the second call