interfaces: safe to assume $realif exists, use it consistently
interfaces: safe to assume $realif exists, use it consistently

get_real_interface() is basically just a large wrap around $wancfg['if'] and
since it's used so much try to avoid touching the 'if' internal here.

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core