Fixup SFP module insertion on the 82599 when insertion happens after
the system is booted and running.

Add PHY detection logic to ixgbe_handle_mod() and add locking to
ixgbe_handle_msf() as well.

PR: 150251
Submitted by: aboyer@averesystems.com
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D3188