hyperv/hn: Increase LRO entry count to 128 by default

hn(4) only has one RX ring currently, so default 8 LRO entries
are too small.

Reviewed by: adrian
Approved by: adrian (mentor)
MFC after: 1 week
Sponsored by: Microsoft OSTC
Differential Revision: https://reviews.freebsd.org/D5166