#3235 imm: option -d does not work when using with option -a in immlist tool

[Thien Minh Huynh]

$ immlist -d '|' -a macAddress dn=1
expect: macAddress=x1:x2:x3:x4|x1:x2:x3:x4
result: macAddress=x1:x2:x3:x4:x1:x2:x3:x4

[Thien Minh Huynh]

commit c539684e0f98b90ef65a031bff17864055fbfeb4 (HEAD -> develop, origin/develop)
Author: thien.m.huynh thien.m.huynh@dektech.com.au
Date: Thu Nov 12 12:39:41 2020 +0700

imm: prevent override delimiter value when using with option -a [#3235]

when using option -d to set delimiter for multiple value combine with
option -a. Delimiter was override with default value. The fix is checking
delimiter option before assign default value.