MINOR: checks: Support mux protocol definition for tcp and http health checks

It is now possible to force the mux protocol for a tcp-check based health check
using the server keyword "check-proto". If set, this parameter overwrites the
server one.

In the same way, a "proto" parameter has been added for tcp-check and http-check
connect rules. If set, this mux protocol overwrites all others for the current
connection.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 08cbff3..3e4be61 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -4411,7 +4411,7 @@
 
 http-check connect [default] [port <expr>] [addr <ip>] [send-proxy]
                    [via-socks4] [ssl] [sni <sni>] [alpn <alpn>] [linger]
-		   [comment <msg>]
+		   [proto <name>] [comment <msg>]
   Opens a new connection to perform an HTTP health check
   May be used in sections :   defaults | frontend | listen | backend
                                  yes   |    no    |   yes  |   yes
@@ -4442,6 +4442,11 @@
                  for instance: "h2,http/1.1". If it is not set, the server ALPN
                  is used.
 
+    proto <name> forces the multiplexer's protocol to use for this connection.
+                 It must be an HTTP mux protocol and it must be usable on the
+                 backend side. The list of available protocols is reported in
+                 haproxy -vv.
+
     linger       cleanly close the connection instead of using a single RST.
 
   Just like tcp-check health checks, it is possible to configure the connection
@@ -10029,7 +10034,7 @@
 
 tcp-check connect [default] [port <expr>] [addr <ip>] [send-proxy] [via-socks4]
                   [ssl] [sni <sni>] [alpn <alpn>] [linger]
-                  [comment <msg>]
+                  [proto <name>] [comment <msg>]
   Opens a new connection
   May be used in sections:   defaults | frontend | listen | backend
                                yes    |    no    |   yes  |   yes
@@ -10060,6 +10065,11 @@
                  for instance: "http/1.1,http/1.0" (without quotes).
                  If it is not set, the server ALPN is used.
 
+    proto <name> forces the multiplexer's protocol to use for this connection.
+                 It must be a TCP mux protocol and it must be usable on the
+                 backend side. The list of available protocols is reported in
+                 haproxy -vv.
+
     linger       cleanly close the connection instead of using a single RST.
 
   When an application lies on more than a single TCP port or when HAProxy
@@ -12535,6 +12545,15 @@
   a comma-delimited list of protocol names, for instance: "http/1.1,http/1.0"
   (without quotes). If it is not set, the server ALPN is used.
 
+check-proto <name>
+  Forces the multiplexer's protocol to use for the server's health-check
+  connections. It must be compatible with the health-check type (TCP or
+  HTTP). It must also be usable on the backend side. The list of available
+  protocols is reported in haproxy -vv.
+  Idea behind this optipon is to bypass the selection of the best multiplexer's
+  protocol for health-check connections established to this server.
+  If not defined, the server one will be used, if set.
+
 check-sni <sni>
   This option allows you to specify the SNI to be used when doing health checks
   over SSL. It is only possible to use a string to set <sni>. If you want to
@@ -12990,7 +13009,6 @@
   set. See also the "addr" parameter.
 
 proto <name>
-
   Forces the multiplexer's protocol to use for the outgoing connections to this
   server. It must be compatible with the mode of the backend (TCP or HTTP). It
   must also be usable on the backend side. The list of available protocols is