kernel: net: phylink: add lock for serializing concurrent pl->phydev writes with resolver

A flaw was found in the Linux kernel’s phylink subsystem: when phylinkresolve executes while pl-statemutex is held, it may acquire pl-phydev-lock out of order relative to other paths phylinkbringupphy or phylinkdisconnectphy that acquire pl-phydev-lock prior to pl-statemutex. This lock inversion...