em(4) does not autonegotiate when fixed media is set

From: J.R. Oldroyd <fbsd_at_opal.com>
Date: Wed, 02 Mar 2022 15:33:31 UTC
An em(4) interface configured with fixed media/mediatype settings, as in:
	ifconfig em0 media 100baseTX mediatype full-duplex
does not respond to autonegotiation from the switch it is connected to.
(Actually, it does for 1000base but not for 100base or 10base.)  As a
result, the switch may end up with mis-matched configuration.

Attached patch enables autonegotiation even when media settings are set
to fixed 100base or 10base.

I am not sure if there should also be:
	hw->phy.autoneg_wait_to_complete = FALSE;
for these 100base and 10base cases to handle the situation where the other
end isn't going to autonegotiate either.