Poll PHY status using internal e6000sw registers

e6000sw family automatically reflects PHY status in each port's registers.
Therefore it is not necessary to do a full PHY polling squence, which
results in much quicker operation and much less significant usage of
the SMI bus.

Care must be taken that the resulting ifmedia_active is identical to
what the PHY will compute, or gratuitous link status changes will
occur whenever the PHYs update function is called.

This patch implements above improvement. On the occasion set a pointer to
the proc structure to be part of software context instead of being
a global variable.

Submitted by: Marcin Wojtas <mw@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Reviewed by: loos
Differential revision: https://reviews.freebsd.org/D10714