Capture the current state of Phabricator Review D1994.

em(4) has multiqueue support, toggle the right compile bits
to enable the support. Update man page with instructions and flush
out missing hw.em tuneables.

Increase the number of MSI-X vectors to 5 for 82574L when used in MQ
mode. (erj@)

Add RSS logic and turn it on in h/w. Inspired and taken from DragonFly emx(4)
driver.

Break up the RX and TX queues into seperate configuration entities. It
is desireable in some cases to have these as seperate knobs. It may be
required on certain adapters for this functionality to work.