iscsi-target: Fix CHAP_A parameter list handling

The target is failing to handle list of CHAP_A key-value pair form
initiator.The target is expecting CHAP_A=5 always. In other cases,
where initiator sends list (for example) CHAP_A=6,5 target is failing
the security negotiation. Which is incorrect.

This patch handles the case (RFC 3720 section 11.1.4).
where in the initiator may send list of CHAP_A values and target replies
with appropriate CHAP_A value in response

(Drop whitespaces + rename to chap_check_algorithm + save original
 pointer + add explicit check for CHAP_A key - nab)

Signed-off-by: Tejas Vaykole <tejas.vaykole@calsoftinc.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>