uqmi: fix network registration loop

uqmi: fix network registration loop

With some debug in qmi.sh using following patch, some errors are visible
in the registration step
@@ -29,6 +29,7 @@ proto_qmi_init_config() {
 }

 proto_qmi_setup() {
+       set -x
        local interface="$1"
        local dataformat connstat plmn_mode mcc mnc
        local device apn auth username password pincode delay modes pdptype
@@ -224,6 +225,8 @@ proto_qmi_setup() {
                fi
        done

+       registration=$(uqmi -s -d "$device" --get-serving-system)
+
        [ -n "$modes" ] && uqmi -s -d "$device" --set-network-modes "$modes" > /dev/null 2>&1

        echo "Starting network $interface"

During the boot of the system, modem could not start automatically its
network registration.
netifd: wan (9235): + echo 'Waiting for network registration'
netifd: wan (9235): Waiting for network registration
netifd: wan (9235): + local 'registration_timeout=0'
netifd: wan (9235): + uqmi -s -d /dev/cdc-wdm1 --get-serving-system
netifd: wan (9235): + grep '"searching"'
netifd: wan (9235): + uqmi -s -d /dev/cdc-wdm1 --get-serving-system
netifd: wan (9235): + registration='{"registration":"not_registered","plmn_mcc":208,"plmn_mnc":20,"plmn_description":"","roaming":true}'
netifd: wan (9235): + '[' -n  ]
netifd: wan (9235): + echo 'Starting network wan'

As the while loop checks only "searching" pattern, uqmi.sh script quits
searching loop and continues whereas the modem is not registered

Other issue, after X seconds modem stops searching.
netifd: wan (9213): + uqmi -s -d /dev/cdc-wdm0 --get-serving-system
netifd: wan (9213): + grep '"searching"'
netifd: wan (9213): + '[' -e /dev/cdc-wdm0 ]
netifd: wan (9213): + '[' 3 -lt 0 -o 0 '=' 0 ]
netifd: wan (9213): + let registration_timeout++
netifd: wan (9213): + sleep 1
netifd: wan (9213): + uqmi -s -d /dev/cdc-wdm0 --get-serving-system
netifd: wan (9213): + grep '"searching"'
netifd: wan (9213): + uqmi -s -d /dev/cdc-wdm0 --get-serving-system
netifd: wan (9213): + registration='{"registration":"not_registered"}'
netifd: wan (9213): + '[' -n  ]
netifd: wan (9213): + echo 'Starting network wan'
netifd: wan (9213): Starting network wan

If registration_timeout is not expired, registration can be restarted

Signed-off-by: Thomas Richard <thomas.richard@kontron.com>
Tested-by: Florian Eckert <fe@dev.tdt.de>
(cherry picked from commit 2eda042d553c23590c9d6ade8a1a17ffcfb4be7c)