BUG/MINOR: dns: dns_connect_server must return -1 unsupported nameserver's type

This patch fix returns code in case of dns_connect_server is called
on unsupported type (which should not happen). Doing this we have
the warranty that after a return 0 the fd is never -1.

This patch should fix github issues #1127, #1128 and #1130
1 file changed