RDMA/core: Remove unused ib_ud_header_unpack

ib_ud_header_unpack() is unused, and I can't see any sign of it
ever having been used in git.  The only reference I can find
is from December 2004 BKrev: 41d30034XNbBUl0XnyC6ig9V61Nf-A when
it looks like it was added.

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://patch.msgid.link/20241221014021.343979-2-linux@treblig.org


Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>