re-set the http2 max streams on settings negotiation.

there was a bug where the max streams in the connection would trigger a
stream limit exceeded, however the check done was based on active
streams that max requests variable from the httpx connection. This is
wrong when peer negotiates more concurrent streams, but is checking the
stream limit against the wrong value received from httpx.

lib/httpx/connection/http2.rb

@@ -43,6 +43,8 @@ module HTTPX
     end
 
     def exhausted?
+      return false if @max_requests.zero? && @connection.active_stream_count.zero?
+
       @connection.active_stream_count >= @max_requests
     end
 
@@ -228,7 +230,11 @@ module HTTPX
     def on_settings(*)
       @handshake_completed = true
 
-      @max_requests = @connection.remote_settings[:settings_max_concurrent_streams] if @max_requests.zero?
+      if @max_requests.zero?
+        @max_requests = @connection.remote_settings[:settings_max_concurrent_streams]
+
+        @connection.max_streams = @max_requests if @connection.respond_to?(:max_streams=) && @max_requests.positive?
+      end
 
       @max_concurrent_requests = [@max_concurrent_requests, @max_requests].min
       send_pending