Normally, when a 'resquery_t' object is created in fctx_query(),
we call dns_adb_beginudpfetch() (which increases the ADB quota)
only if it's a UDP query. Then, in fctx_cancelquery(), we call
dns_adb_endudpfetch() to decreases back the ADB quota, again only
if it's a UDP query.
The problem is that a UDP query can become a TCP query, preventing
the quota from adjusting back in fctx_cancelquery() later.
Call dns_adb_beginudpfetch() also when switching the query type
from UDP to TCP.
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