[FROG] bgpd as0 rfc7607 compliance

[Joe Maimon]

Seems to be finding plenty of these

AGGREGATOR attribute is BGP_AS_ZERO(0)

However, rfc7607 specifies error handling as per rfc7606 which suggests 
most frequently the withdrawn treatment

bgpd appears to instead proceed for ebgp peers and notify for ibgp 
sessions, I am curious as to how either of these are correct and would 
appreciate any advice on the matter.

Frustratingly, I haven't figured out any good way to log which prefix 
update are triggering this.

Best,

Joe