bump ABI version again

1.10 and 1.11 both introduced incompatible changes to the
libiscsi ABI.  Please do not do that, and feel free to Cc
me on any patch that touches include/.  In the meanwhile,
bump the soname of the library.  I suggest releasing 1.11.1
with this change for distros.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>