mss/mtu: make all size calculations use size_t

mss/mtu: make all size calculations use size_t

Half of them used unsigned int, the other half size_t.
Standardize on one. Could've also standardized on the
other, both are much too big for the expected numbers
anyway.

Add a new utility function clamp_size_to_int for
cases we need to change from size_t to int (there
are a lot of those all over our codebase).

Resolves some -Wconversion warnings.

Change-Id: Ic996eca227d9e68279a454db93fcbc86a7bd0380
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Message-Id: <20231008104022.20200-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/search?l=mid&q=20231008104022.20200-1-frank@lichtenheld.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>