Rename rtpav1 plugin to just rtp

Cargo.toml

meson.build

net/rtp/Cargo.toml

net/rtp/build.rs

net/rtp/src/av1/common/aggr_header.rs

net/rtp/src/av1/common/error.rs

net/rtp/src/av1/common/integers.rs

net/rtp/src/av1/common/mod.rs

net/rtp/src/av1/common/obu.rs

net/rtp/src/av1/depay/imp.rs

net/rtp/src/av1/depay/mod.rs

net/rtp/src/av1/mod.rs

net/rtp/src/av1/pay/imp.rs

net/rtp/src/av1/pay/mod.rs

net/rtp/src/lib.rs

net/rtp/tests/rtpav1.rs