Filter sru_z3950: set init sz to 10 M

Filter sru_z3950: set init sz to 10 M

Increase values of {preferredMessage,maximumRecord}Size for Init
Requests generated by sru_z3950 from 1 to 10 megabytes. SRU don't
have these parameters and in most cases we don't care or don't want
backends to return partial results. However, since comstack by
default don't allow more than 5 MB by default and since packages
are all in memory we can't increase too much.