[DOC] Clarify that global pooling is going to reset padding (#15269)
[DOC] Clarify that global pooling is going to reset padding (#15269)

This behaviour changed from older MXNet versions in which global pooling
would consider padding. This clarifies the user documentation.

See also #14421
tlby/mxnet,eric-haibin-lin/mxnet,apache/incubator-mxnet,DickJC123/mxnet,sxjscience/mxnet,tlby/mxnet,yajiedesign/mxnet,zhreshold/mxnet,tlby/mxnet,szha/mxnet,eric-haibin-lin/mxnet,DickJC123/mxnet,larroy/mxnet,zhreshold/mxnet,eric-haibin-lin/mxnet,larroy/mxnet,reminisce/mxnet,larroy/mxnet,apache/incubator-mxnet,eric-haibin-lin/mxnet,yajiedesign/mxnet,sxjscience/mxnet,zhreshold/mxnet,yajiedesign/mxnet,larroy/mxnet,szha/mxnet,ForkedReposBak/mxnet,yajiedesign/mxnet,leezu/mxnet,reminisce/mxnet,reminisce/mxnet,larroy/mxnet,reminisce/mxnet,apache/incubator-mxnet,tlby/mxnet,tlby/mxnet,szha/mxnet,yajiedesign/mxnet,larroy/mxnet,zhreshold/mxnet,leezu/mxnet,DickJC123/mxnet,sxjscience/mxnet,ForkedReposBak/mxnet,eric-haibin-lin/mxnet,sxjscience/mxnet,tlby/mxnet,yajiedesign/mxnet,reminisce/mxnet,DickJC123/mxnet,reminisce/mxnet,larroy/mxnet,leezu/mxnet,zhreshold/mxnet,yajiedesign/mxnet,szha/mxnet,ForkedReposBak/mxnet,sxjscience/mxnet,leezu/mxnet,sxjscience/mxnet,ForkedReposBak/mxnet,sxjscience/mxnet,eric-haibin-lin/mxnet,zhreshold/mxnet,yajiedesign/mxnet,larroy/mxnet,reminisce/mxnet,tlby/mxnet,szha/mxnet,ForkedReposBak/mxnet,yajiedesign/mxnet,tlby/mxnet,tlby/mxnet,tlby/mxnet,reminisce/mxnet,leezu/mxnet,szha/mxnet,sxjscience/mxnet,zhreshold/mxnet,reminisce/mxnet,larroy/mxnet,apache/incubator-mxnet,szha/mxnet,szha/mxnet,leezu/mxnet,leezu/mxnet,ForkedReposBak/mxnet,szha/mxnet,eric-haibin-lin/mxnet,eric-haibin-lin/mxnet,zhreshold/mxnet,sxjscience/mxnet,ForkedReposBak/mxnet,eric-haibin-lin/mxnet,zhreshold/mxnet,leezu/mxnet,reminisce/mxnet,leezu/mxnet,ForkedReposBak/mxnet,ForkedReposBak/mxnet