The `mb_map full' message is output when something tries to allocate a
mbuf cluster but there's no room left in the virtual address region
assigned to mbuf clusters.

This is not supposed to be fatal, but...

You can increase the space allotted for mbuf clusters by defining
NMBCLUSTERS in your config file.  e.g.:

options		"NMBCLUSTERS=1024"

(In -current, you don't need the quotes.)