IL17F and brain infarction: Reduced brain infarct volume, improved neurological function, reduced BBB and intestinal permeability, suppressed neuroinflammation and intestinal inflammation by improving the dysregulation of intestinal microflora, increasing the abundance of Lachnospiraceae, Treponema, Lactobacillus, Ruminococcaceae and Prevotellaceae_NK3B31_group, and decreasing the abundance of Bacteroides, and inhibiting the IL‐17F/TRAF6/NF‐κB pathway