Add missing include for TLSSocket

[marcuschangarm]

Description

TCP and UDP sockets are automatically available when mbed.h is
included in an application.

This change lets the TLSSocket be used in the same way.

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[cmonr]

Makes sense to me.

[NirSonnenschein]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3540
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8621/

Triggering tests

/morph test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 3151
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8621/

[mbed-ci]

Test : FAILURE

Build number : 3324
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8621/3324

[cmonr]

/morph test

[mbed-ci]

Test : FAILURE

Build number : 3328
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8621/3328

[0xc0170]

/morph test

[mbed-ci]

Test : SUCCESS

Build number : 3330
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8621/3330

[cmonr]

Tricky tricky. TLSSocket is not in 5.10.
#8775 (comment)