DEVEL15-afsd-allow-maxmtu-override-20090530

DEVEL15-afsd-allow-maxmtu-override-20090530

LICENSE IPL10
FIXES 124880

rxi_Findcbi, rxi_FIndIfnet, rxi_FindIfMTU "failure" end up returning
the RX_REMOTE_PACKET_SIZE as the mtu to use unless we allow our override
to apply, so we do that. then, add an afsd switch to allow setting it.

afsd man page update required and will follow.

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This delta was composed from multiple commits as part of the CVS->Git migration.
The checkin message with each commit was inconsistent.
The following are the additional commit messages.
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LICENSE IPL10
FIXES 124880

man page update to document previous work

(cherry picked from commit 74df876dafb9cf80ab5a8099b4202f2205bd9791)