brcmfmac: increase message buffer size for control packets

In wifi firmware, max length of IOCTL/IOVAR buffer size is 8192.
Increase the message buffer max size same as wifi firmware for control
packets so return buffers can come back.

Signed-off-by: Soontak Lee <soontak.lee@cypress.com>
Signed-off-by: Jia-Shyr Chuang <joseph.chuang@cypress.com>
Signed-off-by: Chi-Hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200610152106.175257-3-chi-hsien.lin@cypress.com