The RA field is absent from management frames (addr1 is DA there), and
addr1 in other frames.
The TA field is absent from management frames (addr2 is SA there), and
addr2, if present, in other frames.
While we're at it, fix a font glitch in the pcap-filter man page.
pcap-linktype man pages; it should be section 7 for UN*Xes using the
V7/BSD conventions (this includes *BSD, Linux, and Mac OS X), and
section 5 for UN*Xes using the System V conventions (this includes
Solaris and HP-UX, and possibly AIX).