mpegts: Define the section length with a constant

The specification says the value is expressed in 10 bits including
the 4-byte CRC.

(cherry picked from commit 89616408e38ac7257e36976723df0e23d6ee1157)
Signed-off-by: Diego Biurrun <diego@biurrun.de>

Conflicts:
	libavformat/mpegtsenc.c
mpegts: Do not try to write a PMT larger than SECTION_SIZE

Prevent out of array writes.

Similar to what Michael Niedermayer did to address the same issue.

Bug-Id: CVE-2014-2263
CC: libav-stable@libav.org

Signed-off-by: Diego Biurrun <diego@biurrun.de>
(cherry picked from commit e8049af1325dd59a51546c15b2e71a0f578e9d27)

Conflicts:
	libavformat/mpegtsenc.c