haproxy: add conflict to packages with SSL or without SSL support

Both packages provide the same packages and should conflict to each
other.

Fixes:
```
Packages 'haproxy' and 'haproxy-nossl' do not conflict while providing same file: /usr/sbin/haproxy
Packages 'haproxy' and 'haproxy-nossl' do not conflict while providing same file: /etc/haproxy.cfg
Packages 'haproxy' and 'haproxy-nossl' do not conflict while providing same file: /etc/init.d/haproxy
```

They should not be installed side by side.

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>

net/haproxy/Makefile

@@ -60,6 +60,7 @@ define Package/haproxy-nossl
   TITLE+=without SSL support
   VARIANT:=nossl
   DEPENDS+= +libpcre +libltdl +zlib +libpthread +liblua5.3 +libatomic
+  CONFLICTS:=haproxy
 endef
 
 define Package/haproxy-nossl/description