ath11k: Advertise MPDU start spacing as no restriction

Adverise MPDU start spacing as no restriction in ht capabilities,
Since IPQ8074 hw support all sorts of mpdu start spcing. With this
observed minor uplink performance improvement in lower data frame
size case with Veriwave clients.

Signed-off-by: Venkateswara Naralasetty <vnaralas@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>