LU-10391 socklnd: don't deref lnet_hdr in LNDs

LU-10391 socklnd: don't deref lnet_hdr in LNDs

The lnd_hdr structure needs to be extended to support larger
addresses.  To assist this we need to minimize the number of places
that its content are accessed.

Currently the internals of lnet_hdr are larely untouched inside the
various LNDs, but there are some exceptions in socklnd.
These exceptions are not necessary - the same data is available from
elsewhere in the lnet_msg.

So change those accesses to use the lnet_msg info instead.

Test-Parameters: trivial
Test-Parameters: serverversion=2.12 serverdistro=el7.9 testlist=runtests
Test-Parameters: clientversion=2.12 testlist=runtests
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ia37548323fafc77df7a42a1ac956c926f1b9ebf9