wifi: iwlwifi: mld: KUnit: create chanctx with a custom width

Currently iwlmld_kunit_add_chanctx receives a band, picks a predefined
static chandef, and creates the chanctx from it.
Change it to receive a bandwidth as well. Otherwise, the bandwidth in
the chanctx/phy will be different than what test specified in the
iwl_mld_kunit_link.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Link: https://patch.msgid.link/20250313002008.85a1285d34cd.Ia71cdcd4241fe73501bc93e3cb2c6bb3f631b9ec@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>