wpa_supplicant: Fix global control interface for STA/STA-FIRST/STA-NEXT

wpa_supplicant: Fix global control interface for STA/STA-FIRST/STA-NEXT

update_stations(ctrl_conn) is stuck in never-ending loop:

sendto(3, "STA-FIRST", 9, 0, NULL, 0)   = 9
pselect6(4, [3], NULL, NULL, {10, 0}, NULL) = 1 (in [3], left {9, 999995000})
recvfrom(3, "UNKNOWN COMMAND\n", 4095, 0, NULL, NULL) = 16
sendto(3, "STA-NEXT UNKNOWN COMMAND", 24, 0, NULL, 0) = 24
pselect6(4, [3], NULL, NULL, {10, 0}, NULL) = 1 (in [3], left {9, 999995833})
recvfrom(3, "UNKNOWN COMMAND\n", 4095, 0, NULL, NULL) = 16
sendto(3, "STA-NEXT UNKNOWN COMMAND", 24, 0, NULL, 0) = 24
pselect6(4, [3], NULL, NULL, {10, 0}, NULL) = 1 (in [3], left {9, 999995000})
recvfrom(3, "UNKNOWN COMMAND\n", 4095, 0, NULL, NULL) = 16
sendto(3, "STA-NEXT UNKNOWN COMMAND", 24, 0, NULL, 0) = 24

Direct STA, STA-FIRST, and STA-NEXT commands from the global control
interface to a per-interface control interface to avoid this.

Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>