qcacld-3.0: Update user PS config after STA connection

For the user power save enable/disable request, host doesn't send power
config to FW if STA is not in connected state. Host remembers users power
save config in MAC context's "usr_cfg_ps_enable" member. So use this
"usr_cfg_ps_enable" to send power save config to FW after STA associates
to AP.
Problem scenario:
1) User brings STA interface up and sends power save enable to host.
2) As kernel expects power save config command success even in the STA is
   in disconnected state, host doesn't send power save config to FW and
   returns success to kernel.
3) If user doesn't send power save enable command to host after STA
   connects to AP. STA remains in full power mode.
Fix:
1) Use "usr_cfg_ps_enable" to send power save config to FW after STA
   connects to AP.

Change-Id: I412567e2bb40a7b2d9566106e50a422f173a86d1
CRs-Fixed: 2767543