repo: Update contact email for Mat Martineau

[mjmartineau]

I'm still using my git.kernel.org repo and am maintaining MPTCP, but my old email address doesn't work any more. Shift over to my kernel.org email.

[matttbe]

Hello,

Just in case this is needed and as written in the MAINTAINERS file, I confirm Mat's email address (martineau@kernel.org)

[rli9]

thanks for the patch