removed exec from script which that prevents the further lines to be …

[kannankvs]

This change fixes the issue "Adding watchdog functionality results in xcvrd not starting"

- What I did
The script "platform/broadcom/sonic-platform-modules-dell/s6100/scripts/s6100_platform.sh" calls the watchdog disable script "/usr/local/bin/platform_watchdog_disable.sh" using "exec", which is incorrect.
When any script is called using "exec" the caller script will not execute any lines after this "exec" lines. Hence, the caller script was not executing the code that starts xcvrd. Hence, the command "sfputil show presence" was always failing.
This "exec" is removed from this line so that the caller script continues to execute the remaining lines.

- How to verify it
Executed "sftputil" and confirmed that it works. Sample log is given below.
root@sonic:~# sfputil show presence
Port Presence

---

Ethernet0 Present
Ethernet1 Present
Ethernet2 Present
Ethernet3 Not present
Ethernet4 Present
Ethernet5 Present
Ethernet6 Not present

root@sonic:~# sfputil show eeprom
Ethernet0: SFP EEPROM detected
Connector: MPOx12
Encoding: 64B66B
Extended Identifier: Power Class 1(1.5W max)
Extended RateSelect Compliance: QSFP+ Rate Select Version 1
Identifier: QSFP+ or later
Length OM3(2m): 50
Nominal Bit Rate(100Mbs): 103
Specification compliance:
10/40G Ethernet Compliance Code: 40GBASE-SR4
Vendor Date Code(YYYY-MM-DD Lot): 2013-06-01
Vendor Name: AVAGO
Vendor OUI: 00-17-6a
Vendor PN: AFBR-79E4Z-D-FT1
Vendor Rev: 01
Vendor SN: 7503836100HL

Ethernet1: SFP EEPROM detected
Connector: MPOx12
Encoding: 64B66B
Extended Identifier: Power Class 1(1.5W max)
Extended RateSelect Compliance: QSFP+ Rate Select Version 1
Identifier: QSFP+ or later
Length OM3(2m): 50
Nominal Bit Rate(100Mbs): 103
Specification compliance:
10/40G Ethernet Compliance Code: 40GBASE-SR4
Vendor Date Code(YYYY-MM-DD Lot): 2014-03-17
Vendor Name: AVAGO
Vendor OUI: 00-17-6a
Vendor PN: AFBR-79EQDZ-FT1
Vendor Rev: 01
Vendor SN: 4829443H007U

Ethernet2: SFP EEPROM detected
Connector: No separable connector
Encoding: Unspecified
Extended Identifier: Power Class 1(1.5W max)
Extended RateSelect Compliance: QSFP+ Rate Select Version 1
Identifier: QSFP+ or later
Length Cable Assembly(m): 1
Nominal Bit Rate(100Mbs): 103
Specification compliance:
10/40G Ethernet Compliance Code: 40GBASE-CR4
Vendor Date Code(YYYY-MM-DD Lot): 2013-02-19
Vendor Name: Amphenol
Vendor OUI: 78-a7-14
Vendor PN: 599690001
Vendor Rev: A
Vendor SN: CN0NWGTV32G4928

Ethernet3: SFP EEPROM not detected

- Description for the changelog
Removed the "exec"