Pull up following revision(s) (requested by skrll in ticket #1698):

sys/dev/usb/ehci.c: revision 1.317

PR 57518: usb keyboard causes host controller to miss microframe

As per the USB 2.0 specification section 11.18.4; paragraph 3.b
For interrupt IN/OUT full-/low-speed transactions, the host must  schedule a
complete-split transaction in each of the two microframes following the
first microframe in which the full-/low-speed transaction is budgeted. An
additional complete-split must also be scheduled in the third following
microframe unless the full-/low-speed transaction was budgeted to start
in microframe Y6.

(martin)