Continuation of lock cleanup in e1000.
Post-cold sleep instead of DELAY when waiting for firmware.
Convert softc mutex to an SX lock. Change all waits to sleeps
once interrupts are enabled (and it is safe to sleep).
Submitted by: Matt Macy <firstname.lastname@example.org>
Sponsored by: Limelight Networks
Differential Revision: https://reviews.freebsd.org/D12101