MFC r260255:

Properly document -u and -s.

Sponsored by:	The FreeBSD Foundation
MFC r260083:

Fix extremely slow operation with data digests enabled.  This was caused
by receive code waiting for data digest even when the data segment was
empty.  It didn't actually read it, but it waited until those four bytes
become available in the socket buffer, i.e. until any other PDU (e.g. NOP)
came in.

Sponsored by:	The FreeBSD Foundation
MFC r260389:

Fix a rare "truncated checksums" problem, which manifested like this:

WARNING: icl_pdu_check_data_digest: data digest check failed; got 0xf23b,
should be 0xdb7f23b

Sponsored by:	The FreeBSD Foundation