lro: separate HPTS specific code into tcp_lro_hpts.c

Put same copyright header as tcp_hpts.c has, since all this code
was developed by Randall Stewart <rrs@FreeBSD.org> as a part of
the HPTS work. Also copy Mellanox copyright from tcp_lro.c as
Hans Petter Selasky also participated in restructuring the code.

Reviewed by: imp, tuexen, rrs
Differential Revision: https://reviews.freebsd.org/D42854

(cherry picked from commit 4f9c93f16c30d553613def0442d8ddbee859e76b)