network.subr: avoid unnecessary reinitialization

Do not start interface when wpa_supplicant or hostapd is used;
they will restart it anyway

Tested with:

• Intel 3945BG, STA mode (wpa_supplicant)
• RTL8188EU, HOSTAP mode (hostapd)

Approved by: adrian (mentor)
Differential Revision: https://reviews.freebsd.org/D5486